The proverbial phrase what’s sauce for the goose is sauce for the gander, and its variants, mean what is appropriate in one case is also appropriate in the other case in question.
The earliest occurrences of this phrase that I have found are as follows, in chronological order:
1-: From A Collection of English Proverbs Digested into a convenient Method for the speedy finding any one upon occasion; with Short Annotations. Whereunto are added Local Proverbs with their Explications, Old Proverbial Rhythmes, Less known or Exotick Proverbial Sentences, and Scottish Proverbs (Cambridge: Printed by John Hayes, Printer to the University, for W. Morden, 1670), by the English naturalist and theologian John Ray (1627-1705):
That that’s good sawce for a goose, is good for a gander.
This is a womans Proverb.
2-: From The English Rogue: Continued in the Life of Meriton Latroon, and other Extravagants. Comprehending the Most Eminent Cheats of Most Trades and Professions (London: Printed for Francis Kirkman, 1671), by the Irish author Richard Head (1637?-1686?):
My Master asked me if I could not invent a way to punish [the maid’s] sloath? I told him I would do my best endeavor; so that day I got some Horse-hair and shred it fit for my purpose, telling my Master what I would do with it; at night when he came home, he sent the maid for two pots of Ale, when she was gone for it, I took my shred hair, and strowed the same in her bed betwixt the sheets, which plagued her worse then if she had had half a peck of six footed vermine to her bedfellows […]. The hair tormented her so abominably, that nolens volens she was forced to rise, and sit up until the morning, when looking in the sheets she found the cause of her disquietness; the cunning Jade made no speech of it at all, but was as pleasant that morning as if she had ailed nothing all night; which made me to mistrust my art, and think I had not done my business right. All that day she was busied with her thoughts in contriving mischief against me, the result whereof was, that she took the sheets from off her bed and laid them on mine, whereby she paid me home in my own coyn, and whereof I could not justly complain, seeing what was sauce for a Goose was sauce for a Gander.
3-: From a letter by Perient Trott, dated 7th September 1675, published in A True Relation of the just and unjust Proceedings of the Somer-Islands-Company: In relation to 20 Shares of Land that Perient Trott bought of the R.t Hon.ble the late Robert Earl of Warwick the 22.th of February 1658 ([s.l.]: [s.n.], 1676):
What is sauce for a goos [sic], is sauce for a gander.
4-: From A Seasonable Addresse to both Houses of Parliament, concerning the Succession, the Fears of Popery, and Arbitrary Government. By a true Protestant and hearty Lover of his Countrey (Edinburgh, Reprinted 1681), by George Savile (1633-1695), 1st Marquess of Halifax:
Remember that the most forward in the Long Parliament, were soon turn’d out by others; and because what is Sawce for a Goose, is Sawce for a Gander, this of course will be the fate of those, who now glory in being Ringleaders of Faction, to thwart and oppose their Sovereign.
5-: From The Third Part of No Protestant Plot: With Observations on the Proceedings upon the Bill of Indictment against the E. of Shaftsbury: And a Brief Account of the Case of the Earl of Argyle (London: Printed for Richard Baldwin, 1682), by the Scottish presbyterian minister, pamphleteer and conspirator Robert Ferguson (died 1714):
There are others, and some of them not only men of Quality, but Wit, who say, That the Witnesses having been believed against the Papists, they ought also to be believed against Protestants; seing [sic], as they are pleased to express it, What is sawce for a Goose is also sawce for a Gander […]. Upon the whole, we shall finde Sawce for their Goose, but in the mean time we defie them to find sawce for their Gander.
6-: From The Observator of 31st October 1682, by the English author and press censor Roger L’Estrange (1616-1704)—(London: Printed by J. Bennet, for William Abington, 1684):
Prethee Whig, Is not Sawce for a Goose, Sawce for a Gander? And is it not much More reasonable for Authority to Punish the Breakers of the Law then for Usurpers to Punish the Asserters of it?
7-: From Three Considerations proposed to Mr. William Pen, Concerning the Validity and Security of his New Magna Charta for Liberty of Conscience, by A. Baptist; which may be worthy the Consideration of all the Quakers, and of all my Dissenting Brethren also that have Votes in the Choice of Parliament-Men (London: [s.n.], 1688?), by the English clergyman Thomas Comber (1645-1699):
Pray M. Pen, Consider what your New Charter can signifie, so long as there is a High Commission Court, or a High Commission for Ecclesiastical Affairs set up? Cannot those Commissioners take any of your and our Preachers, Teachers, or Ministers to task when they please? Cannot they when they have a mind to it, Suspend Mr. Pen, or George Whitehead, M. Alsop, Mr. Lobb, or Mr. Mead, or Mr. Bowyer, as well as the Bishop of London, D. Sharp, or D. Doughty? Notwithstanding your New Charter? Cannot the Court when they will, or shall think fit, or be commanded, Suspend, Silence, or forbid any or all the Dissenting Ministers to Preach any longer in their Meetings, if they will not read any Declaration or Order whatever, that the King shall set forth and require them to Read? Remember the Magdalen Colledge-Men, Remember also that Sawce for a Goose is or may be Sawce for a Gander.
8-: From Observations upon Mr. Johnson’s Remarks, upon Dr. Sherlock’s Book of Non-Resistance (London: [s.n.], 1689), by William Sherlock (1641?-1707), Church of England clergyman and religious controversialist:
Let any man in the world judge, whether this be any more than fair turning of the Tables, and giving just the same Sauce to the Goose, that you gave to the Gander.
9-: From Providence and Precept: Or, The Case of doing Evil that Good may come of it, Stated and Resolved; According to Scripture, Reason, and the (Primitive) Practice of the Church of England. With a more particular Respect to a Late Case of Allegiance, &c. and its Vindication. In a Letter to the Author (London: [s.n.], 1691), by Mr. Richardson:
’Tis true, you say God is not confined to humane Laws, but at the same time ’tis reasonable to suppose though he be not, you and I, and all Mankind are; and the acting or doing any thing against humane Laws, (especially such which do not contradict his) is the same thing as breaking of God’s Laws. And no doubt the doing so, is a Resisting the Higher Power, and they that Resist shall (as you say) receive to themselves Damnation: And if so, What is Sawce for a Goose, is Sawce for a Gander.
10-: From A Brief History of Presbytery and Independency, From their first Original, to this Time. Shewing, Wherein, and the Reasons why they Separate from the Church of England. Wherein they differ from each other. With Some Remarks on the late Heads of Agreement, Assented to by the United Ministers of both Perswasions. Written at the Request, and for the Satisfaction of a Private Friend, and now made publick for General Information (London: Printed for Edward Faulkner, 1691):
Now let the Mouth of this battering Cannon be but turn’d against the Church of England, as ’tis there against the Church of Rome, it will assuredly give as loud a Report, and do as much Execution for us in justifying our Separation as well as theirs; Seeing there are Imposed on us, Doubtful things for certain, &c. And we think this is ground enough for us, as well as for themselves, not to Embrace the Communion of such a Church: Why may not our (we think so) be as good as their (we think so?) Why may not our Rouland be as good as their Oliver? What is good Sawce for a Goose, may be as good Sawce for a Gander, &c.
11-: From Fables, of Æsop and other Eminent Mythologists: With Morals and Reflexions (London: Printed for R. Sare, T. Sawbridge, B. Took, M. Gillyflower, A. & J. Churchil, and J. Hindmarsh, 1692), by the English author and press censor Roger L’Estrange (1616-1704):
FAB. CCCII. A Husband and Wife twice Marry’d.
There happen’d a Match betwixt a Widower, and a Widow. The Woman would be perpetually Twitting of her second Husband, what a Man her First was; and her Husband did not forget the Ringing of it in her Ears as often, what an Admirable Woman he had to his First Wife. As the Woman was One day upon the Peevish Pin, a Poor Body comes to the Door, while the Froward Fit was upon her, to beg a Charity. Come in Poor Man (says the Woman) Here’s e’en the Leg of a Capon for thee to pray for the Soul of my First Husband. Nay, faith, says the Husband, and when thy Hand is In, e’en take the Body and the Rest on’t, to pray for the Soul of My First Wife. This was Their way of Teizing One Another, and of Starving the Living to the Honour of the Dead; for they had but That One Capon betwixt them to Supper.
Sauce for a Goose is Sauce for a Gander. There’s no Contending with the Laws of God and Man, Especially against Those that have Power, and Right on their Sides.
12-: From Deo Ecclesiæ & Conscientiæ Ergo: Or, A Plea for Abatement in Matters of Conformity, to several Injunctions and Orders of the Church of England. To which are added some Considerations of the Hypothesis of a King de Jure and de facto, proving that King William is King of England, &c. as well of Right as Fact, and not by a bare Actual Possession of the Throne (London: Printed for Richard Baldwin, 1693), by Iræneus Junior, “a Conforming Member of the Church of England”:
Was it not an hard case for those Earls and Noblemen abovesaid to be accounted guilty of a capital Crime, for presenting their Petition for a redress of Grievances? Nor was it much better with us when the late Abhorrences were in fashion, by which they had so far decried, that reasonable and undoubted liberty of the Subject; which the late King believing, and that the Sauce for a Goose might serve for a Gander too, took the advantage of imprisoning and impeaching the Seven Bishops for a modest and humble Representation of their Grievances, which by the Law of the Land they were sufficiently vouched to do. But Laws it seems are Fetters which no Princes must be intangled with, if our Hyperconformists Divinity be good.
13-: From Bibliotheca Politica: Or An Enquiry into the Ancient Constitution of the English Government; Both in respect to the just extent of Regal Power, and the Rights and Liberties of the Subject. Wherein all the Chief Arguments, as well against, as for the late Revolution, are impartially Represented, and considered, in Thirteen Dialogues. Collected out of the Best Authors, as well Antient as Modern (London: printed for R. Baldwin, 1694), by the English political philosopher James Tyrell (1642-1718):
I may safely […] affirm, That an Unjust Conquest gives the Conqueror no Right to the Subjects Obedience, much less over their Lives or Estates; and if our Norman William and his Successors had no more Right to the Crown of England than meer Conquest, I doubt whether they might have been driven out, after the same manner they came in: But I believe you will find, upon second thoughts, that unjust Conquests and Usurpations of Crowns, to be no firm Titles for Princes to rely on; lest the old English Proverb be turned upon you, viz. That which is Sauce for a Goose, is Sawce for a Gander.
14-: From Some General Proverbs, in The Compleat Book of Knowledge: Treating of the Wisdom of the Antients (London: Printed by W. Onley, 1698):
That that’s sauce for a Goose, is sauce for a Gander.
15-: From The Assembly of Women, Or, The Female Parliament, in Seven New Colloquies Translated out of Erasmus Roterodamus. As also the Life of Erasmus. By Mr. Brown (London: Printed for Charles Brome, 1699):
Pray Madam why should not we be allowed to talk freely of the Men, since they make no scruple of saying what they please of their Wives. You know the Proverb, What is Sawce for a Goose, is Sawce for a Gander.