Genesis 38:3 (KJV)

And it came to pass at that time, that Judah went down from his brethren, and turned in to a certain Adullamite, whose name was Hirah.

And Judah saw there a daughter of a certain Canaanite, whose name was Shuah; and he took her, and went in unto her.

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.