Only choose in marriage a woman whom you would choose as a friend if she were a man.

[Il faut ne choisir pour épouse que la femme qu’on choisirait pour ami, si elle était homme.]

Joseph Joubert (1754-1824) French moralist, philosopher, essayist, poet

Pensées [Thoughts], ch. 8 “De la Famille et de la Société, etc. [On the Family and Society],” ¶ 9 (1850 ed.) [tr. Collins (1928), ch. 7]
    (Source)

(Source (French)). Alternate translations:

We should choose for a wife only the woman we should choose for a friend, were were she a man.
[tr. Calvert (1866), ch. 8]

One ought not to choose for a wife a woman whom one would not choose for a friend, were she a man.
[tr. Attwell (1896), ¶ 98]

One should only choose for a wife a woman whom one would choose for a friend, were she a man.
[tr. Lyttelton (1899), ch. 7, ¶ 4]

Do not choose for your wife any woman you would not choose as your friend if she were a man.
[tr. Auster (1983)], 1801]