Deuteronomy 25:5-6
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5If brothers dwell together, and one of them die, and have 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 to him as wife, and perform the duty of a husband`s brother to her. 6It 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.
Deuteronomy 25:5-6 (WEB)