The unanimous Belief of Muslim world is that Prophet Muhammad (صلى الله عليه وسلم) is the Last and Final Messenger/Prophet of Allah. In other words Prophet-hood has ended with Prophet Muhammad (صلى الله عليه وسلم) and those who do not believe in it are ventured out of the bounds of Islam. 

The first and foremost factor of Imān is respect for the Rasūl sallAllāhu álayhi wa sallam. Salāh or any form of ‘ibādah is useless without reverence for the Beloved Rasūl şallAllāhu álayhi wa sallam. There are many ‘Abd-Allah’s [servants of Allah Almighty] in this world, but the true and sincere ‘Abd-Allah is he, who is ‘Abde-Mustafa [servant of the Beloved Prophet sallAllāhu álayhi wa sallam]. If it is not so, then he is surely an ‘Abde-Shaytan [servant of the cursed devil]. May the Merciful Allah Almighty save us all from this curse! [Ameen!]