Deuteronomy 25:5-7

5If brothers live together and one of them dies without having a son, the dead man’s wife must not remarry someone outside the family. Instead, her late husband’s brother must go to her, marry her, and perform the duty of a brother-in-law.

6Then the first son she bears will continue the name of the dead brother, thus preventing his name from being blotted out of Israel.

7But if the man does not want to marry his brother’s widow, then she must go to the elders at the town gate and say, “My husband’s brother refuses to preserve his brother’s name in Israel; he is unwilling to perform the duty of a brother-in-law to me!”