Deuteronomy 25:4-6

New International Version - UK

⁴ Do not muzzle an ox while it is treading out the grain.

⁵ If brothers are living together and one of them dies without a son, his widow must not marry outside the family. Her husband’s brother shall take her and marry her and fulfil the duty of a brother-in-law to her. ⁶ The first son she bears shall carry on the name of the dead brother so that his name will not be blotted out from Israel.