If brethren dwell together, and one of them dies, and has no child, the wife of the dead shall not marry outside unto a stranger: her husband's brother shall go in unto her, and take her to him as wife, and perform the duty of a husband's brother unto her.
All Commentaries on Deuteronomy 25:5 Go To Deuteronomy 25
Augustine of Hippo
AD 430
In the third book, then, when I was solving the question of how it was possible for Joseph to have two fathers, I indeed said that “he was begotten by one and adopted by the other.” But I should have mentioned too the kind of adoption, for what I said sounds as if another living father had adopted him. The law, however, also adopted the children of the deceased by ordering that “a brother marry the wife” of his childless, deceased brother and “raise up seed” by the same woman “for his deceased brother.” In this way the explanation of this matter of the two fathers of one man is indeed made clearer. .