וַיֵּ֣דַע אוֹנָ֔ן כִּ֛י לֹּ֥א ל֖וֹ יִהְיֶ֣ה הַזָּ֑רַע וְהָיָ֞ה אִם־בָּ֨א אֶל־אֵ֤שֶׁת אָחִיו֙ וְשִׁחֵ֣ת אַ֔רְצָה לְבִלְתִּ֥י נְתָן־זֶ֖רַע לְאָחִֽיו׃
오난이 그 씨가 자기 것이 되지 않을 줄 알므로 형수에게 들어갔을 때에 형에게 아들을 얻게 아니하려고 땅에 설정하매
Targum Jonathan on Genesis
And Onan knew that they would not call the children after his name, and it was, when he entered to the wife of his brother, that he corrupted his work upon the earth, that he might not raise up children to his brother's name.