Numbers 20:10

Assembled, etc. This is one of the places where a small area held a large multitude.

Can we extract from this rock? Because they did not recognize it, as the rock settled itself among the other rocks when the well departed. The Israelites were telling them, “What [difference] is it to you, from which rock you extract water for us”? This is why he addressed them as “rebels “—”insolents,” “fools” in Greek. Those who instruct their instructors. Can we extract water from this rock for which we were not commanded?

And Mosheh and Aharon gathered the congregation together before the rock. And Mosheh said to them, Hear now, rebels: is it possible for us to bring forth water for you from this rock?

ARE WE TO BRING YOU FORTH WATER OUT OF THIS ROCK? Far be it and [G-d] forbid that [we should explain this] as a question indicating impossibility! For Moses our teacher, who was trusted in all G-d’s house, [knew] that nothing is too hard for Him; and he together with all Israel had seen greater and more wondrous miracles than this, and especially since this [miracle of providing water from a rock] had already been done once before through him at the rock in Horeb! Now the commentators have said that there are certain questions which [by apparently doubting that which cannot be denied], have the force of an [impassioned or indignant] affirmation. Thus we find: Did I reveal Myself to the house of thy father?; The sense is: “Did I not reveal Myself, although your sons, by their actions appear to belie it!” The king said also unto Zadok the priest: ‘Seest thou?’; Wilt thou judge?; Hast thou eaten of the tree, whereof I commanded thee that thou shouldest not eat? But Rabbi Abraham ibn Ezra wrote [that the meaning of the verse is]: “Do we indeed have power to bring you forth water out of the rock?” He means thereby to explain that Moses said to them: “Hear now, ye rebels against G-d, who say, ‘and why have ye brought the assembly of the Eternal unto this evil place?’, Verse 5. Do we have the power by natural means to bring you forth water out of this flint? You should therefore recognize that this is all from G-d, for it is He Who took you out of Egypt, and brought you to this place, and it is He Who will feed you here.” This is similar to what he [Moses] told the people in the case of the manna, and ye shall know that the Eternal hath brought you out from the land of Egypt.
In my opinion this letter hei [in the word hamin — “out of”] indicates a [real] query, [and the meaning thereof is as follows]: “Are we to bring you forth water out of this rock or not?” For sometimes Scripture explains a question in its positive and negative aspects, such as: whether there are trees therein or not? whether thou wouldest keep His commandments, or not? — and at other times it mentions only the positive aspect, [such as in the following verses]: Is this your youngest brother?; Know ye Laban the son of Nachor?;, 29:5. Should I weep in the fifth month, separating myself? But this question here that Moses asked of them was a probing question [to …

ויאמר להם שמעו נא המורים, just as this staff produced almonds as a reminder of the last rebellious generation, are we to produce water from you from this rock?

At the time he raised the staff he struck it twice in succession followed by saying :did you really think that we would produce water from this rock?” Moses said this because he harboured doubt; seeing that G’d had instructed him to take the staff with him (verse 8) he did not think that speaking to the rock was meant to result in the rock yielding up its water, but that striking it may be required, just as he had done at Refidim.
As to the fact that G’d had specifically instructed him to “speak” to the rock, he thought that speaking to a rock, i.e. communicating one’s thoughts to it, consisted of striking the rock. In the absence of certainty about which course to follow, Moses decided to speak to the rock in addition to striking it, but G’d had already indicated that He accepted Moses’ striking the rock by making all that water come forth.
In spite of G’d’s apparent approval of what Moses had done he was punished, seeing that G’d employs more stringent rules in dealing with the righteous such as Moses than He applies to ordinary mortals. This is what He meant when he said in verse 12 “because you did not demonstrate faith in Me to use this opportunity to sanctify Me by means of first having spoken to the rock.”
“Seeing that I, the commentator, am aware that Moses was quite incapable of deliberately countermanding G’d’s instructions, I had to explain the episode as resulting from an error Moses made.”