He himself claimed to have received the word of Qur'an. His previous life was a proof of his honesty and truthfulness. By and by people were convinced and they believed in him.
Quran
Quran is God revelation and His words to prophet Muhammad through the Angel Gabriel. Hadith is prophet Muhammad saying.
First of all, the words are not Muhammad's (PBUH) they are ALLAH's (God's) words and the name of the book is "The Holy Quran"more info could be found here:http://en.wikipedia.org/wiki/Quran
That would be the Koran or Quran.
Quran talked only about some aspects of prophet Muhammad (PBUH) life that could be guides to Muslims. Quran is real God words as revealed to prophet Muhammad and not containing historical chapters written by some followers as in the Bible.
Gabriel (or Jibril) is the angel who conveyed God words of Quran to prophet Muhammad (PBUH).
Hadith is prophet Muhammad (PBUH) saying. Quran is real God words revealed to prophet Muhammad (PBUH) through the Angel Gabriel (Jibril). Hadith text may be different in wording according to narrator precision and capacity of memorising exactly prophet Muhammad words. However, Quran is preserved over years without single letter alteration or change as they are real God words preserved by God.
Prophet Muhammad (peace be upon him) started receiving God revelation of Quran through the angel Gabriel in year 610 AD (when he was 40 years old).
The words are God words revelation to prophet Muhammad through the Angel Gabriel (Jibril). The Quran revelation continued from year 610 AD through year 632 AD. God named these words as 'Quran'. The Angel Gabriel (Jibril) revised with the prophet Muhammad, twice a year except the last year it was only once, the ordering and arrangements of the Quran verses .
Muslims have Quran as their holy book. Muslims pay all respect to Quran as their holy book that reflects real God words revelation to prophet Muhammad (PBUH) and that guides them, together with prophet Muhammad teachings, to the right path to God and to God worship. Refer to question below on why was Quran revealed.
The Prophet Muhammad (Peace be upon him) was described by his noble wife, 'Aa'ishah (May Allah be pleased with her)as a "walking Quran": in other words, he didn't just read and recite the Quran, he lived it.
The Muslims's sacred book is called Quran. Quran is real God words revelation to prophet Muhammad (PBUH) through the angel Gabriel (Jibril).