Genesis – The Story of Er, Onan and Tamar
Genesis 38:8-10
After Er dies childless, Judah instructs Onan to fulfill levirate duty so that seed may be raised up for his dead brother — a narrative that underlies the halakhic and ethical concern for posthumous progeny, and the gravity of preventing it.
וַיֹּ֤אמֶר יְהוּדָה֙ לְאוֹנָ֔ן בֹּ֛א אֶל־אֵ֥שֶׁת אָחִ֖יךָ וְיַבֵּ֣ם אֹתָ֑הּ וְהָקֵ֥ם זֶ֖רַע לְאָחִֽיךָ׃ וַיֵּ֣דַע אוֹנָ֔ן כִּ֛י לֹּ֥א ל֖וֹ יִהְיֶ֣ה הַזָּ֑רַע וְהָיָ֞ה אִם־בָּ֨א אֶל־אֵ֤שֶׁת אָחִיו֙ וְשִׁחֵ֣ת אַ֔רְצָה לְבִלְתִּ֥י נְתׇן־זֶ֖רַע לְאָחִֽיו׃ וַיֵּ֛רַע בְּעֵינֵ֥י יְהֹוָ֖ה אֲשֶׁ֣ר עָשָׂ֑ה וַיָּ֖מֶת גַּם־אֹתֽוֹ׃
Then Judah said to Onan, “Join with your brother’s wife and do your duty by her as a brother-in-law, and provide offspring for your brother.” But Onan, knowing that the offspring would not count as his, let [the semen] go to waste whenever he joined with his brother’s wife, so as not to provide offspring for his brother. What he did was displeasing to GOD, who took his life also.