Never cut what you can untie.

[Ne coupez pas ce que vous pouvez dénouer.]

Joseph Joubert (1754-1824) French moralist, philosopher, essayist, poet
Pensées [Thoughts], ch. 9 “De la Sagesse, de la Vertu, etc. [On Wisdom and Virtue],” ¶ 10 (1850 ed.) [tr. Calvert (1866)]
    (Source)

(Source (French)). Alternate translations:

Never cut what you can unravel.
[tr. Lyttelton (1899), ch. 8, ¶ 10]

Don't cut what you can untie.
[tr. Auster (1983), 1797 entry]