When brothers dwell together and one of them dies without a son, the widow must not marry outside the family. Her husband’s brother is to take her as his wife and fulfill the duty of a brother-in-law for her.
KJV
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.
ASV
If brethren dwell together, and one of them die, and have no son, the wife of the dead shall not be married 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 a husband’s brother unto her.