Genesis 43:32

And they set on for him by himself, and for them by themselves, and for the Egyptians which did eat with him by themselves; because the Egyptians might not eat bread with the Hebrews; for that is an abomination unto the Egyptians. Cf Deuteronomy 12:17; Deuteronomy 16:5; Deuteronomy 17:15. Although they all ate in the same room, they were served at different tables, as the rules of the caste required. Joseph belonged to the priestly caste and could therefore not sit down at the same table with laymen, and the Egyptians would not eat at the same table with members of a nomad tribe.