Muhammad (c. 570 – 8 June 632 CE) was an Arab religious, military and political leader and the founder of Islam. According to Islam, he was a prophet who was divinely inspired to preach and confirm the monotheistic teachings of Adam, Noah, Abraham, Moses, Jesus, and other prophets. He is believed by Muslims to be the Seal of the Prophets, and along with the Quran, his teachings and normative examples form the basis for Islamic religious belief.

Muhammad was born in Mecca to the aristocratic Banu Hashim clan of the Quraysh. He was the son of Abdullah ibn Abd al-Muttalib and Amina bint Wahb. His father, Abdullah, the son of tribal leader Abd al-Muttalib ibn Hashim, died around the time Muhammad was born. His mother Amina died when he was six, leaving Muhammad an orphan. He was raised under the care of his grandfather, Abd al-Muttalib, and paternal uncle, Abu Talib. In later years, he would periodically seclude himself in a mountain cave named Hira for several nights of prayer. When he was 40, in c. 610, Muhammad reported being visited by Gabriel in the cave and receiving his first revelation from God. In 613, Muhammad started preaching these revelations publicly, proclaiming that "God is One", that complete "submission" (Islām) to God (Allāh) is the right way of life (dīn), and that he was a prophet and messenger of God, similar to other prophets in Islam.

Muhammad's followers were initially few in number, and experienced persecution by Meccan polytheists for 13 years. To escape ongoing persecution, he sent some of his followers to Abyssinia in 615, before he and his followers migrated from Mecca to Medina (then known as Yathrib) later in 622. This event, the Hijrah, marks the beginning of the Islamic calendar, also known as the Hijri calendar. In Medina, Muhammad united the tribes under the Constitution of Medina. In December 629, after eight years of intermittent fighting with Meccan tribes, Muhammad gathered an army of 10,000 Muslim converts and marched on the city of Mecca. The conquest went largely uncontested, and Muhammad seized the city with minimal casualties. In 632, a few months after returning from the Farewell Pilgrimage, he fell ill and died. By the time of his death, most of the Arabian Peninsula had converted to Islam.

The revelations (waḥy) that Muhammad reported receiving until his death form the verses (āyah) of the Quran, upon which Islam is based, and are regarded by Muslims as the verbatim word of God and his final revelation. Besides the Quran, Muhammad's teachings and practices, found in transmitted reports, known as hadith, and in his biography (sīrah), are also upheld and used as sources of Islamic law. Apart from Islam, Muhammad has received praise in Sikhism as an inspirational figure, in the Druze faith as one of the seven main prophets, and in the Baháʼí Faith as a Manifestation of God.

Important early sources for the life of Muhammad are authors from the 2nd and 3rd centuries AH (overlapping with the 8th and 9th centuries CE), whose works supplied additional biographical information to the Muslim traditions regarding his life.

The earliest written sira (biographies of Muhammad and quotes attributed to him) is Ibn Ishaq's Life of God's Messenger written c. 767 (150 AH). Although the original work was lost, this sira survives as extensive excerpts in works by Ibn Hisham and to a lesser extent by al-Tabari. However, Ibn Hisham wrote in the preface to his biography of Muhammad that he omitted matters from Ibn Ishaq's biography that "would distress certain people". Another early historical source is the history of Muhammad's campaigns by al-Waqidi (d. 207 AH), and the work of Waqidi's secretary Ibn Sa'd al-Baghdadi (d. 230 AH). Due to these early biographical efforts, more is known about Muhammad than almost any other founder of a major religion. Many scholars accept these early biographies as authentic. However, Waqidi's biography has been widely criticized by Islamic scholars for his methods, in particular his decision to omit his sources. Recent studies have led scholars to distinguish between traditions touching legal matters and purely historical events. In the legal group, traditions could have been subject to invention while historic events, aside from exceptional cases, may have been subject only to "tendential shaping". Other scholars have criticized the reliability of this method, suggesting that one cannot neatly divide traditions into purely legal and historical categories.

Other important sources include the hadith collections, accounts of verbal and physical teachings and traditions attributed to Muhammad. Hadiths were compiled several generations after his death by Muslims including Muhammad al-Bukhari, Muslim ibn al-Hajjaj, Muhammad ibn Isa at-Tirmidhi, Abd ar-Rahman al-Nasai, Abu Dawood, Ibn Majah, Malik ibn Anas, al-Daraqutni.

Muslim scholars have typically placed a greater emphasis on the hadith instead of the biographical literature, since hadith maintain a traditional chain of transmission (isnad); the lack of such a chain for the biographical literature makes it unverifiable in their eyes. The hadiths generally present an idealized view of Muhammad. Western scholars have expressed skepticism regarding the verifiability of these chains of transmission. It is widely believed by Western scholars that there was widespread fabrication of hadith during the early centuries of Islam to support certain theological and legal positions, and it has been suggested that it is "very likely that a considerable number of hadiths that can be found in the hadith collections did not actually originate with the Prophet". In addition, the meaning of a hadith may have drifted from its original telling to when it was finally written down, even if the chain of transmission is authentic. Overall, some Western academics have cautiously viewed the hadith collections as accurate historical sources, while the "dominant paradigm" in Western scholarship is to consider their reliability suspect. Scholars such as Wilferd Madelung do not reject the hadith which have been compiled in later periods, but judge them in their historical context.