And Onan knew that the seed should 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 that he should give seed to his brother.
Berean Study Bible (BSB) - Genesis 38:9 >But Onan knew that the offspring would not belong to him; so whenever he would sleep with his brother’s wife, he would spill his seed on the ground so that he would not produce offspring for his brother.