Deuteronomy 25:5-7

5If brethren shall dwell together, and one of them shall die, and have no child, the wife of the dead shall not marry outside the family to a stranger: her husband’s brother shall go in to her, and take her to him for a wife, and perform the duty of an husband’s brother to her.1 6And it shall be, that the firstborn which she beareth shall succeed in the name of his brother who is dead, that his name may not be blotted out from Israel. 7And if the man shall not desire to take his brother’s wife, then let his brother’s wife go up to the gate to the elders, and say, My husband’s brother refuseth to raise up to his brother a name in Israel, he will not perform the duty of my husband’s brother.2