Deuteronomy 25:5-7

5If brothers are living together and one of them dies without a son, his widow must not marry outside the family. Her husband’s brother shall take her and marry her and fulfill the duty of a brother-in-law to her.

6The first son she bears shall carry on the name of the dead brother so that his name will not be blotted out from Israel.

7However, if a man does not want to marry his brother’s wife, she shall go to the elders at the town gate and say, “My husband’s brother refuses to carry on his brother’s name in Israel. He will not fulfill the duty of a brother-in-law to me.”