Numbers 20:12

יען לא האמנתם בי BECAUSE YE BELIEVED ME NOT — Scripture discloses the fact that but for this sin alone, they would have entered the land of Canaan, in order that people should not say of them, “Even as the sin of the generation of the Wilderness (a term used of those who left Egypt) on whom it was decreed that they should not enter the Land was the sin of Moses and Aaron” (cf. Rashi on Numbers 27:13). But was not the doubting question (cf. Rashi on Numbers 11:22), “shall the sheep and oxen be slaughtered for them?” a more grievous lack of faith in God than this? But because that had been said in private (no Israelites being present and therefore it could have no evil influence upon them), Scripture (God) spared him (and did not make his lack of faith public by pronouncing punishment for it), but here, where all Israel were standing by, Scripture does not spare him because of the Hallowing of the Divine Name (cf. Midrash Tanchuma, Chukat 10). להקדישני TO SANCTIFY ME — For had you spoken to the rock and it had brought forth water I would have been sanctified before the whole congregation, for they would have said: What is the case with this rock which cannot speak and cannot hear and needs no maintenance? It fulfils the bidding of the Omnipresent God! How much more should we do so? לכן לא תביאו THEREFORE YE SHALL NOT BRING — This expression (“therefore”) is used by way of an oath, just as (I Samuel 3:14), “Therefore I have sworn to the house of Eli”. Here He was quick to take an oath in order that they should not pray at length about it (that He should withdraw the decree) (Midrash Tanchuma, Vaera 2).

וַיֹּ֣אמֶר יְהֹוָה֮ אֶל־מֹשֶׁ֣ה וְאֶֽל־אַהֲרֹן֒ יַ֚עַן לֹא־הֶאֱמַנְתֶּ֣ם בִּ֔י לְהַ֨קְדִּישֵׁ֔נִי לְעֵינֵ֖י בְּנֵ֣י יִשְׂרָאֵ֑ל לָכֵ֗ן לֹ֤א תָבִ֙יאוּ֙ אֶת־הַקָּהָ֣ל הַזֶּ֔ה אֶל־הָאָ֖רֶץ אֲשֶׁר־נָתַ֥תִּי לָהֶֽם׃

And the Lord spoke to Moshe and Aharon, Because you did not believe in me, to sanctify me in the eyes of the children of Yisra᾽el, therefore you shall not bring this congregation in to the land which I have given them.