Genesis 38:9-11

Onan knew that the child (heir) would not be his [but his dead brother’s]; so whenever he lay with his brother’s widow, he spilled his seed on the ground [to prevent conception], so that he would not give a child to his brother. But what he did was displeasing in the sight of the LORD; therefore He killed him also [in judgment]. Then Judah said to Tamar, his daughter-in-law, “Remain a widow at your father’s house until Shelah my [youngest] son is grown”; [but he was deceiving her] for he thought that [if Shelah should marry her] he too might die like his brothers did. So Tamar went and lived in her father’s house.