Genesis 38:9

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.

Onan knew that the seed wouldn't be his; and it happened, when he went in to his brother's wife, that he spilled it on the ground, lest he should give seed to his brother.

And Onan knew that the seed would 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 he should give seed to his brother.

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;

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.