Deuteronomy 25:5-9

5“If brothers are living together and one of them dies without a son, the widow of the deceased shall not be married outside the family to a stranger. Her husband’s brother shall be intimate with her after taking her as his wife and perform the duty of a husband’s brother to her.

6It shall be that her firstborn [son] will be given the name of the dead brother, so that his name will not be blotted out of Israel.

7But if the man does not want to marry his brother’s [widowed] wife, then she shall go up to the gate [of the city, where court is held] to the elders, and say, ‘My brother-in-law refuses to continue his brother’s name in Israel; he is not willing to perform the duty of a husband’s brother.’

8Then the elders of his city will summon him and speak to him. And if he stands firm and says, ‘I do not want to marry her,’

9then his brother’s widow shall approach him in the presence of the elders, and pull his sandal off his foot and spit in his face; and she shall answer and say, ‘So it is done to that man who does not build up his brother’s household.’