Why did Moses (peace be upon him) wish to be part of the Ummah of Muhammad (peace be upon him) after learning of its virtues in the Tablets?

The summary of the Fatwa is: The story of Iblis prostrating on Adam's grave was narrated by Qatadah, Wahb ibn Munabbih, and Ka'b al-Ahbar, which indicates that it was taken from the People of the Book. It was also reported in Tarikh Dimashq as being attributed to the Prophet (peace and blessings be upon him) with a weak chain of narration.