Genesis 38:9-11

Darby Translation

⁹ But when Onan knew that the seed should not be his own, it came to pass when he went in to his brother's wife, that he spilled [it] on the ground, in order to give no seed to his brother.

¹⁰ And the thing which he did was evil in the sight of Jehovah, and he slew him also.

¹¹ And Judah said to Tamar his daughter-in-law, Remain a widow in thy father's house, until Shelah my son is grown; for he said, Lest he die also, as his brethren. And Tamar went and remained in her father's house.