Why were Moses and Abraham (peace be upon them) astonished by the prophethood of Prophet Muhammad (peace be upon him) when they met him in the heavens, even though they had met him and he had led them in prayer as an Imam in Jerusalem before that?

The angels are the ones who ask, "Or has he been sent for this?" at each heaven, not the prophets whom the Prophet, peace and blessings be upon him, met. Scholars have mentioned two interpretations regarding the meaning of this question: the first is that it is a question about his being sent for the ascension to heaven, and the second is that it is a question about his being sent to humanity. Ibn Hajar is of the view that the wisdom behind the question is to inform the Prophet, peace and blessings be upon him, that he is known among the Heavenly Host.