Muslims believe that the holy Quran was orally revealed by God to the final Prophet, Muhammad, through the archangel Gabriel, incrementally over a period of some 23 years, beginning on 22 December 609 CE, when Muhammad was 40, and concluding in 632, the year of his death. Muslims regard the Quran as Muhammad's most important miracle, a proof of his prophethood, and the culmination of a series of divine messages starting with those revealed to Adam and ending with Muhammad. The word “Quran” occurs some 70 times in the Quran's text, and other names and words are also said to refer to the Quran.