Numbers 36

Numbers 36:6

Eusebius of Caesarea: Now, since the genealogy of Joseph is so traced, Mary also appears virtually to have been of the same tribe as he, since, according to the law of Moses, intermarriages between different tribes were not permitted. For it was commanded to join in marriage with one of the same family and of the same people, so that the inheritance of the race might not be changed from tribe to tribe. — ECCLESIASTICAL HISTORY 1.7