GEN1086 If he were not a prophet, it would not be necessary to return her? – This is the meaning: “Return the wife of the man,” and as to your saying: “Did he not say to me: ‘She is my sister’? he is a prophet and has divined your motives from your deportment.  If a visitor comes to a city, is it customary to ask him: “Is she your wife or your sister”! From here it is to be derived that a Noachide incurs the death penalty in such instances of capital offense where he could have learned the truth and did not. Makkoth 96 TEMIMAH-GEN 94