Genesis 38:9-11

Young's Literal Translation

⁹ and Onan knoweth that the seed is not [reckoned] his; and it hath come to pass, if he hath gone in unto his brother's wife, that he hath destroyed [it] to the earth, so as not to give seed to his brother;

¹⁰ and that which he hath done is evil in the eyes of Jehovah, and He putteth him also to death.

¹¹ And Judah saith to Tamar his daughter-in-law, `Abide a widow at thy father's house, till Shelah my son groweth up;' for he said, `Lest he die -- even he -- like his brethren;' and Tamar goeth and dwelleth at her father's house.