Genesis 38:6

3 And she conceived, and bare a son; and he called his name Er.

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

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

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

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

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

9 And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother's wife, that he spilled it on the ground, lest that he should give seed to his brother.