It is therefore not true that against nature there is neither rein nor master. On the contrary, there are two of them: one is good manners, the other reason.

[Non è adunque vero che incontro alla natura non abbia freno né maestro: anzi ve ne ha due, ché l’uno è il costume e l’altro è la ragione.]

Giovanni della Casa (1503-1556) Florentine poet, author, diplomat, bishop

Galateo: Or, A Treatise on Politeness and Delicacy of Manners [Il Galateo overo de’ costumi], ch. 25 (1558) [tr. Eisnbichler/Bartlett (1986)]
    (Source)

(Source (Italian)). Alternate translations:

It is not then true, that there is not a bridell and Master for Nature, Nay, she is guided and ruled by twaine: Custome I meane, and Reason.
[tr. Peterson (1576)]

Which being so, it is not true, that we are not furnished with reins, or a proper guide against the impetuosity of our nature: for we have two; one of which is Experience, and the other right Reason.
[tr. Graves (1774)]