Genesis 38:7-9

American Standard Version

⁷ And Er, Judah’s first-born, was wicked in the sight of Jehovah; and Jehovah slew him. ⁸ And Judah said unto Onan, Go in unto thy brother’s wife, and perform the duty of a husband’s brother unto her, and raise up seed to thy brother. ⁹ And Onan knew that the seed would 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.