Deuteronomy 25:5-6

New American Standard Bible

⁵ “When brothers live together, and one of them dies and has no son, the wife of the deceased shall not be married outside the family to a strange man. ^(A)Her husband’s brother shall have relations with her and take her to himself as his wife, and perform the duty of a husband’s brother to her. ⁶ It shall then be that the firstborn to whom she gives birth shall ^[a]assume the name of his father’s deceased brother, so that ^(B)his name will not be wiped out from Israel.