Is there a Quranic or Prophetic text that confirms the absolute stillness of mountains, or is the saying of some commentators about their movement based on other evidence?

Allah created mountains to stabilize the earth so it would not quake, describing them as firm and pegs, which indicates their steadfastness and deep roots. This does not contradict their very slight movement, which is only noticeable with instruments. As for the verse: (And you see the mountains, thinking them solid, but they are passing as clouds pass), the correct interpretation is that it speaks about the Day of Resurrection, when mountains will be uprooted and removed from their places, and not about the Earth's rotation, as some have claimed. This is supported by the context of the verses, which speak about the Day of Resurrection.