Genesis 38:9-11

Living Bible

⁹ But Onan was not willing to have a child who would not be counted as his own, and so, although he married her,^[a] whenever he went in to sleep with her, he spilled the sperm on the bed to prevent her from having a baby which would be his brother’s. ¹⁰ So far as the Lord was concerned, it was very wrong of him to deny a child to his deceased brother, so he killed him, too. ¹¹ Then Judah told Tamar, his daughter-in-law, not to marry again at that time, but to return to her childhood home and to her parents, and to remain a widow there until his youngest son, Shelah, was old enough to marry her. (But he didn’t really intend for Shelah to do this, for fear God would kill him, too, just as he had his two brothers.) So Tamar went home to her parents.