Genesis 38:6-9

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

7But Er, Judah’s firstborn, was wicked in the Lord’s sight; so the Lord put him to death.

8Then Judah said to Onan, “Sleep with your brother’s wife and fulfill your duty to her as a brother-in-law to raise up offspring for your brother.”

9But Onan knew that the child would not be his; so whenever he slept with his brother’s wife, he spilled his semen on the ground to keep from providing offspring for his brother.