Genesis 38:4-8

Then she conceived again and gave birth to a son, and she named him Onan.

She gave birth to yet another son and named him Shelah; and it was at Chezib that she gave birth to him.

Now Judah took a wife for Er his firstborn, and her name was Tamar.

But Er, Judah’s firstborn, was evil in the sight of the Lord, so the Lord took his life.

Then Judah said to Onan, “Have relations with your brother’s wife and perform your duty as a brother-in-law to her, and raise up a child for your brother.”