Genesis 38:7-8, 10-11

But Er was a wicked man in the LORD’s sight, so the LORD took his life. Then 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.”

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