Genesis

⁴And she conceived again, and bare a son; and she called his name Onan. ⁵And she yet again bare a son, and called his name Shelah: and he was at Chezib, when she bare him. ⁶And Judah took a wife for Er his firstborn, and her name was Tamar. ⁷And Er, Judah's firstborn, was wicked in the sight of the Lord; and the Lord slew him. ⁸And Judah said unto Onan, Go in unto thy brother's wife, and perform the duty of an husband's brother unto her, and raise up seed to thy brother. ⁹And 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 he should give seed to his brother. ¹⁰And the thing which he did was evil in the sight of the Lord: and he slew him also.