Genesis 38:8, 11, 26
Then Judah said to Onan, "Sleep with your brother's wife. Perform your duty as her brother-in-law and raise up offspring for your brother." . . .

Deuteronomy 25:5-10
When brothers dwell together and one of them dies without a son, the widow must not marry outside the family. Her husband's brother is to take her as his wife and fulfill the duty of a brother-in-law for her. . . .

Ruth 1:11, 12
But Naomi replied, "Return home, my daughters. Why would you go with me? Are there still sons in my womb to become your husbands? . . .