Genesis 38:7-11

7And Er, Judah’s firstborn, was wicked in the sight of the LORD; and the LORD slew him.

8And Judah said unto Onan, Go in unto thy brother’s wife, and perform the duty of an husband’s brother unto her, and raise up seed to thy brother.

9And 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 he should give seed to his brother.

10And the thing which he did was evil in the sight of the LORD: and he slew him also.

11Then said Judah to Tamar his daughter in law, Remain a widow in thy father’s house, till Shelah my son be grown up: for he said, Lest he also die, like his brethren. And Tamar went and dwelt in her father’s house.