Buddha kept silent about God. This means that God is beyond words, mind and logic as said in the Veda. Buddha means the Buddhi or Jnana yoga that speaks about the absolute God. Thus He is the greatest incarnation of God. If one thinks Him as atheist, there can be no better fool. Mohammed showed the formless medium in which God exists, which is energy and this is presented by Shankara, because basically energy and awareness are one and the same. The prophet itself means human incarnation. Prophet is carrying on the message of God. The divine knowledge is in Him. Is He not greater than other human beings? Message of divine knowledge is the characteristic of God (Satyam Jnanam – the Veda) and so we say God is in Him. Why do you deny it, when God is omnipresent? Then every human being should give the same message of God, since God is omnipresent. But why Mohammed alone gave it? Because the power of God or knowledge of God is in him only. Then the power of God, in the form of knowledge is not omnipresent.
In any case, you have to accept that either God or His Power is only in Prophet Mohammed. That is what human incarnation is. You are fighting with us, without analysing the concept of human incarnation. Thus Buddha, Mohammed and Shankara have made the single phase, which was essential to the level of the followers at that time. The concept of human incarnation was well established by Krishna and Jesus. You can find all three branches of Hinduism (Advaita, Visishta Advaita, Dvaita) in Christianity because Jesus told that He and God are one and the same (Advaita), that He is the son of God (Visishta Advaita) and that He is the messenger of God (Dvaita). The stage of philosophy was expressed according to the required stage of the people of that time.