The Word of the Holy Prophet Muhammad was the Revealed Word of God
The Holy Prophet Muhammad spoke nothing but the revelation from the Lord. This unique character, or exclusive distinction, of the Holy Prophet has been declared by the Holy Qur'an as well as in the ancient Scriptures:
Nor does he speak of (his own) inclination; It (the wording) is naught but a revelation revealed (unto him.)
The Holy Prophet has been identified as such even in ancient Scriptures:
For Moses truly said unto the fathers, a Prophet shall the Lord your God raise unto you of your brethren like unto me; him shall ye hear in all things whatsoever he shall say unto you.
And it shall come to pass that every soul which will not hear "that Prophet" shall be destroyed from among the people.
I will raise them up a Prophet from among their brethren like unto thee, and will put my words in his mouth; and he shall speak unto them all that I shall command him.
And it shall come to pass that whosoever will not hearken unto my words which he shall speak in my name, I will require it of him. (Deuteronomy 18:18, 19)
Howbeit, when the Spirit of Truth is come, he will guide you unto all truth for he shall not speak of himself but whatsoever he shall hear, that shall he speak; he will show you things to come. (St John's Gospel, 16:13)