Genesis 38:7-9

Revised Standard Version

⁷ But Er, Judah’s first-born, was wicked in the sight of the Lord; and the Lord slew him. ⁸ Then Judah said to Onan, “Go in to your brother’s wife, and perform the duty of a brother-in-law to her, and raise up offspring for your brother.” ⁹ But Onan knew that the offspring would not be his; so when he went in to his brother’s wife he spilled the semen on the ground, lest he should give offspring to his brother.