Genesis 38:6-8

6In the course of time, Judah arranged for his firstborn son, Er, to marry a young woman named Tamar.

7But Er was a wicked man in the Lord’s sight, so the Lord took his life.

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.”