Genesis 38:7-9

New International Version - UK

⁷ But Er, Judah’s firstborn, was wicked in the Lord’s sight; so the Lord put him to death.

⁸ Then Judah said to Onan, ‘Sleep with your brother’s wife and fulfil your duty to her as a brother-in-law to raise up offspring for your brother.’ ⁹ But Onan knew that the child would not be his; so whenever he slept with his brother’s wife, he spilled his semen on the ground to avoid providing offspring for his brother.