Charles Ellicott Commentary Numbers 20:10

"And Moses and Aaron gathered the assembly together before the rock, and he said unto them, Hear now, ye rebels; shall we bring you forth water out of this rock?" — Numbers 20:10 (ASV)

Must we fetch you water out of this rock?— In the case of the former miracle at Rephidim the rock is spoken of only under the Hebrew word zur (Exodus 17:6). Throughout the present narration the rock is invariably spoken of under the word sela. In Psalms 78:15-16, where reference appears to be made to both miracles, both words are used.