Genesis 38:6-9

6Judah got a wife for Er, his firstborn, and her name was Tamar.

7Now Er, Judah’s firstborn, was evil in the Lord’s sight, and 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 produce offspring for your brother.”

9But Onan knew that the offspring would not be his, so whenever he slept with his brother’s wife, he released his semen on the ground so that he would not produce offspring for his brother.