Genesis:38:8-9
strkjv@Genesis:38:8 @ And Judah said unto Onan, Go in unto thy brothers wife, and marry her, and raise up seed to thy brother.
strkjv@Genesis:38:9 @ And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brothers wife, that he spilled it on the ground, lest that he should give seed to his brother.