וַיֵּ֣דַע אוֹנָ֔ן כִּ֛י לֹּ֥א ל֖וֹ יִהְיֶ֣ה הַזָּ֑רַע וְהָיָ֞ה אִם־בָּ֨א אֶל־אֵ֤שֶׁת אָחִיו֙ וְשִׁחֵ֣ת אַ֔רְצָה לְבִלְתִּ֥י נְתָן־זֶ֖רַע לְאָחִֽיו׃
俄南知道這後裔不歸他自己，所以每當他與他哥哥的妻子同房的時候，就洩在地上，免得給他哥哥留下後裔。
On the Unchangeableness of God
[16] Some there are who through self-love have brought upon themselves not only defeat but death. Thus Onan “perceiving that the seed will not be his” (Gen. 38:9), ceased not to destroy the reasoning principle, which in kind is the best of all existing things, till he himself underwent utter destruction. And right just and fitting was his fate.
On the Posterity of Cain and his Exile
[180] The chief representative of this doctrine is Onan, kinsman of the leathern Er. For it says “this man knowing that the seed should not be for him, when he went in to his brother’s wife, spilled it on the ground” (Gen. 38:9), going beyond all bounds in love of self and love of pleasure.