Genesis 38:8-10

Darby Translation

⁸ Then Judah said to Onan, Go in to thy brother's wife, and fulfil to her the brother-in-law's duty, and raise up seed to thy brother.

⁹ But when Onan knew that the seed should not be his own, it came to pass when he went in to his brother's wife, that he spilled [it] on the ground, in order to give no seed to his brother.

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