Genesis 38:8-11

8Then Judah said to Er’s brother Onan, “Go and marry Tamar, as our law requires of the brother of a man who has died. You must produce an heir for your brother.”

9But Onan was not willing to have a child who would not be his own heir. So whenever he had intercourse with his brother’s wife, he spilled the semen on the ground. This prevented her from having a child who would belong to his brother.

10But the Lord considered it evil for Onan to deny a child to his dead brother. So the Lord took Onan’s life, too.

11Then Judah said to Tamar, his daughter-in-law, “Go back to your parents’ home and remain a widow until my son Shelah is old enough to marry you.” (But Judah didn’t really intend to do this because he was afraid Shelah would also die, like his two brothers.) So Tamar went back to live in her father’s home.