Charles Ellicott Commentary Numbers 20:8

"Take the rod, and assemble the congregation, thou, and Aaron thy brother, and speak ye unto the rock before their eyes, that it give forth its water; and thou shalt bring forth to them water out of the rock; so thou shalt give the congregation and their cattle drink." — Numbers 20:8 (ASV)

Take the rod. —Some have supposed, from the fact that the rod is represented as being taken from before the Lord (Numbers 20:9), that the reference is to Aaron’s rod, which was kept before the testimony (Numbers 17:10).

On the other hand, the natural presumption is that the rod was the same one with which some of the previous miracles in Egypt, at the Red Sea, and at Rephidim had been performed. This presumption is confirmed by two facts: first, Aaron’s name is not mentioned in this verse until after the mention of the rod; and second, Moses is said, in Numbers 20:11, to have struck the rock with his rod.