Genesis 38:2–10

²There Judah saw the daughter of a Canaanite man named Shua, and he took her as a wife and slept with her. ³So she conceived and gave birth to a son, and Judah named him Er. ⁴Again she conceived and gave birth to a son, and she named him Onan. ⁵Then she gave birth to another son and named him Shelah; it was at Chezib that she gave birth to him.

⁶Now Judah acquired a wife for Er, his firstborn, and her name was Tamar. ⁷But Er, Judah’s firstborn, was wicked in the sight of the LORD; so the LORD put him to death. ⁸Then Judah said to Onan, “Sleep with your brother’s wife. Perform your duty as her brother-in-law and raise up offspring for your brother.”

⁹But Onan knew that the offspring would not belong to him; so whenever he would sleep with his brother’s wife, he would spill his seed on the ground so that he would not produce offspring for his brother. ¹⁰What he did was wicked in the sight of the LORD, so He put Onan to death as well.