Deuteronomy 25:5-6

Expanded Bible

⁵ If two brothers are living together, and one of them dies without having a son, his widow must not marry ·someone [a stranger] outside her husband’s family. Her husband’s brother must marry her, which is his duty to her as a brother-in-law. ⁶ The first son she has ·counts as the son of the dead [will raise up the name of his] brother so that his name will not be ·forgotten [blotted/wiped out] in Israel [Gen. 38; Ruth 4].