Deuteronomy 24:4

24:4 her first husband who divorced her is not permitted to remarry her after she has become ritually impure, for that is offensive to the Lord. You must not bring guilt on the land which the Lord your God is giving you as an inheritance.

Deuteronomy 25:5

Respect for the Sanctity of Others

25:5 If brothers live together and one of them dies without having a son, the dead man’s wife must not remarry someone outside the family. Instead, her late husband’s brother must go to her, marry her, and perform the duty of a brother-in-law.