Quotation על במדבר 20:37

יען לא האמנתם בי, the sin consisted in their saying: המן הסלע הזה נוציא לכם מים?, “Are we to extract water for you from this rock?” They should have said instead: יוציא ה' לכם מים, “G’d will extract water for you.” (verse 10). In Exodus 16,8 Moses had been careful to phrase the announcement of the forthcoming phenomenon of manna by attributing it to coming directly from G’d. Similarly, when predicting any of the other miracles which had been announce beforehand, Moses had carefully attributed the miracle to G’d. By failing to do so this time they left the way open for some of the people to think that the water when it would gush forth would be the result of Moses’ and Aaron’s combined knowledge.
This is also the meaning of the words (Moses quoting G’d) לא קדשתם אותי, “you have not sanctified Me” (Deuteronomy 32,51). On the first occasion, almost 40 years earlier, when water would be produced from a rock, (Exodus 17,6) G’d had introduced the miracle by announcing: “Here I will be standing there before you on the rock at Chorev. Strike the rock and water will issue from it and the people will drink. And Moses did so in the sight of the elders of Israel.” The seventy elders had observed the cloud of glory moving to above the site of that rock so that the miracle became a public spectacle, lending additional greatness to G’d’s name as the provider. In this instance the people did not observe any evidence of G’d’s involvement so that it was easy to conclude, based on Moses’ and Aaron’s phrasing it, that they themselves had initiated this phenomenon.