From al-Malfūdh Sharif, pg 86:

The first and foremost factor of Imān is respect for the Rasūl şallAllāhu 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 şallAllāhu 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!]