Targum for Genesis 38:9
וַיֵּ֣דַע אוֹנָ֔ן כִּ֛י לֹּ֥א ל֖וֹ יִהְיֶ֣ה הַזָּ֑רַע וְהָיָ֞ה אִם־בָּ֨א אֶל־אֵ֤שֶׁת אָחִיו֙ וְשִׁחֵ֣ת אַ֔רְצָה לְבִלְתִּ֥י נְתָן־זֶ֖רַע לְאָחִֽיו׃
And Onan knew that the seed would not be his; and it came to pass when he went in unto his brother’s wife, that he spilled it on the ground, lest he should give seed to his brother.
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.
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