Does the Prophet’s — may God’s prayers and peace be upon him — refusal to allow the two mountains to collapse on the people of Mecca, and his not taking revenge for himself, indicate that he is more merciful than God, taking into account that God sometimes takes revenge?

The understanding that a created being could be more merciful than the Creator is refuted by the texts. The Holy Quran describes Allah Almighty as "the Most Merciful of the merciful," as also mentioned in the supplications of the prophets Ayyub, Ya'qub, and Musa, peace be upon them.

In Sahih Muslim, it is evident that Allah is "the Most Merciful of the merciful" as He, out of His absolute mercy, brings out of the Fire those who have never done any good.

Although the Prophet, peace and blessings be upon him, is described with mercy and compassion, his mercy is a part of Allah Almighty's mercy and a grace from Him, Glorified be He, as He made him gentle and merciful towards his Ummah. Thus, no one is more merciful than Allah Almighty.