Deuteronomy 25:5-10

If two brothers are living together, and one of them dies without having a son, his widow must not marry someone outside her husband’s family. Her husband’s brother must marry her, which is his duty to her as a brother-in-law. The first son she has counts as the son of the dead brother so that his name will not be forgotten in Israel. But if a man does not want to marry his brother’s widow, she should go to the elders at the town gate. She should say, “My brother-in-law will not carry on his brother’s name in Israel. He refuses to do his duty for me.” Then the elders of the town must call for the man and talk to him. But if he is stubborn and says, “I don’t want to marry her,” the woman must go up to him in front of the leaders. She must take off one of his sandals and spit in his face and say, “This is for the man who won’t continue his brother’s family!” Then that man’s family shall be known in Israel as the Family of the Unsandaled.