One of my friends holds that the Holy Prophet (sws) is dead. He is no more in this world. We should not pray to Allah with his reference. For example we cannot say: O God, please forgive me because of your beloved Prophet (sws). He says we should plead to Allah directly. Mohammad (sws) is dead and the dead have no value. This is unacceptable and heartrending to me. Please explain how he can be rebutted.