And Moses sent to call Dathan and Abiram... — If, as seems probable from Numbers 16:3, Dathan and Abiram had joined Korah and his company in the address to Moses which is contained in Numbers 16:3, they must have subsequently withdrawn themselves and retired to their own tents, from which they refused to go up at the bidding of Moses.
Related Commentaries of Numbers 16:12
Numbers 16:12
12 And Moses sent to call Dathan and Abiram, the sons of Eliab: which said, We will not come up: