And Judah said to Onan, "Go in to your brother's wife and marry her, and raise up an heir to your brother."
Genesis 38:8
Surrounding context
38:7 But Er, Judah's firstborn, was wicked in the sight of the LORD, and the LORD killed him.
38:8 And Judah said to Onan, "Go in to your brother's wife and marry her, and raise up an heir to your brother."
38:9 But Onan knew that the heir would not be his; and it came to pass, when he went in to his brother's wife, that he emitted on the ground, lest he should give an heir to his brother.