Deuteronomy 25:5-9

5When 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.1 6The first son she bears will carry on the name of the dead brother, so that his name will not be blotted out from Israel.

7But if the man does not want to marry his brother’s widow, she is to go to the elders at the city gate and say, “My husband’s brother refuses to preserve his brother’s name in Israel. He is not willing to perform the duty of a brother-in-law for me.”

8Then the elders of his city shall summon him and speak with him. If he persists and says, “I do not want to marry her,” 9his brother’s widow shall go up to him in the presence of the elders, remove his sandal, spit in his face, and declare, “This is what is done to the man who will not maintain his brother’s line.”