Genesis 38:4-8

And she conceived again, and bare a son; and she called his name Onan.

And she yet again conceived, and bare a son; and called his name Shelah: and he was at Chezib, when she bare him.

And Judah took a wife for Er his firstborn, whose name was Tamar.

And Er, Judah’s firstborn, was wicked in the sight of the LORD; and the LORD slew him.

And Judah said unto Onan, Go in unto thy brother’s wife, and marry her, and raise up seed to thy brother.