Deuteronomy 25:5-7

5If brethren dwell together, and one of them die, and have no son, the wife of the dead shall not marry without unto a stranger: her husband’s brother shall go in unto her, and take her to him to wife, and perform the duty of an husband’s brother unto her.

6And it shall be, that the firstborn which she beareth shall succeed in the name of his brother which is dead, that his name be not blotted out of Israel.

7And if the man like not to take his brother’s wife, then his brother’s wife shall go up to the gate unto the elders, and say, My husband’s brother refuseth to raise up unto his brother a name in Israel, he will not perform the duty of an husband’s brother unto me.