Genesis 38:6-9

6Then Judah got a wife for Er, his firstborn, and her name was Tamar.

7But Er, Judah’s firstborn, was evil in Adonai’s eyes, so Adonai put him to death.

8Then Judah said to Onan, go to your brother’s wife to perform the duty of a brother-in-law to her, and raise up a seed for your brother.

9But Onan knew that the seed would not be his. So every time he went to his brother’s wife he would destroy it on the ground so as not to provide a seed for his brother.