Deuteronomy 25:5 in the King James Version
If brethren dwell together, and one of them die, and have no child, 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.
Context
4 You shall not muzzle the ox when he treads out the grain.
5 If brothers dwell together, and one of them dies and has no son, the wife of the dead shall not be married outside to a stranger. Her husband’s brother shall go in to her, and take her as his wife, and perform the duty of a husband’s brother to her.
6 It shall be that the firstborn whom she bears shall succeed in the name of his brother who is dead, that his name not be blotted out of Israel.