Companions of the Prophet in the context of "Abu Bakr"

In the Islamic study of hadith, an isnād (chain of transmitters, or literally "supporting"; Arabic: اِسْناد) refers to a list of people who passed on a tradition, from the original authority to whom the tradition is attributed to, to the present person reciting or compiling that tradition. The tradition an isnad is associated with is called the matn. Isnads are an important feature of the genre of Islamic literature known as hadith and are prioritized in the process that seeks to determine if the tradition in question is authentic or inauthentic.

According to the traditional Islamic view, the tradition of the hadith sciences has succeeded in the use of isnads to distinguish between authentic and inauthentic traditions going back to Muhammad and his companions. The contemporary view in modern hadith studies, however, is that isnads were commonly susceptible to forgery and so had to be scrutinized before being used to guarantee the transmission of a tradition.

The Saqifa (Arabic: سَقِيفَة, romanized: Saqīfah) of the Banu Sa'ida clan refers to the location of an event in early Islam where some of the companions of the Islamic prophet Muhammad pledged their allegiance to Abu Bakr as the first caliph and successor to Muhammad shortly after his death in 11 AH (632 CE). The Saqifa meeting is among the most controversial events in early Islam, due to the exclusion of a large number of Muhammad's companions, including his immediate family and notably Ali, his cousin and son-in-law. The conflicts that arose soon after Muhammad's death are considered to be the main cause of the current division among Muslims. Those who accepted Abu Bakr's caliphate were later labeled Sunnis, while the supporters of Ali's right to caliphate were later labeled Shia.

Shia Islam is the second-largest branch of Islam. It holds that Muhammad designated Ali ibn Abi Talib (r. 656–661) as both his political successor (caliph) and as the spiritual leader of the Muslim community (imam). However, his right is understood to have been usurped by a number of Muhammad's companions at the meeting of Saqifa, during which they appointed Abu Bakr (r. 632–634) as caliph instead. As such, Sunni Muslims believe Abu Bakr, Umar (r. 634–644), Uthman (r. 644–656) and Ali to be 'rightly-guided caliphs', whereas Shia Muslims regard only Ali as the legitimate successor.

Shia Muslims believe that the imamate continued through Ali's sons, Hasan and Husayn, after which various Shia branches developed and recognized different imams. They revere the ahl al-bayt, the family of Muhammad, maintaining that they possess divine knowledge. Shia holy sites include the shrine of Ali in Najaf, the shrine of Husayn in Karbala, and other mausoleums of the ahl al-bayt. Later events, such as Husayn's martyrdom in the Battle of Karbala (680 CE), further influenced the development of Shia Islam, contributing to the formation of a distinct religious sect with its own rituals and shared collective memory.

Umar ibn al-Khattab (Arabic: عُمَر بْن ٱلْخَطَّاب, romanized: ʿUmar ibn al-Khaṭṭāb; c. 584 – 644), also spelled Omar, was the second Rashidun caliph, ruling from August 634 until his assassination in 644. He succeeded Abu Bakr (r. 632–634) and is regarded as a senior companion and father-in-law of the Islamic prophet Muhammad.

Initially, Umar opposed Muhammad, who was his distant Qurayshite kinsman. However, after converting to Islam in 616, he became the first Muslim to openly pray at the Kaaba. He participated in nearly all of Muhammad’s battles and expeditions, and Muhammad conferred upon him the title al-Fārūq ("the Distinguisher") for his sound judgement. After Muhammad’s death in June 632, Umar pledged allegiance to Abu Bakr as the first caliph and served as his chief adviser. In 634, shortly before his death, Abu Bakr nominated Umar as his successor.

Uthman ibn Affan (Arabic: عُثْمَان بْن عَفَّان, romanized: ʿUthmān ibn ʿAffān) (c. 573 or 576 – 17 June 656) was the third caliph of the Rashidun Caliphate, ruling from 644 until his assassination in 656. Uthman, a second cousin, son-in-law, and senior companion of the Islamic prophet Muhammad, played a major role in early Islamic history. During his reign as caliph, he was known for ordering the official compilation of the standardized version of the Quran, known as Uthman's Quran, that is still being used today.

Before his predecessor, caliph Umar (r. 634–644) died in office, he appointed a committee of trustees to elect a successor. Uthman, who was then aged 68–71 years, was elected to succeed him and became the oldest person to hold such a high position. During his premiership, the Caliphate expanded further into Persia and reached as far as the provinces of Khorasan and Transoxiana in the East as well as Ifriqiya and the Iberian Peninsula in the West. Uthman instituted centralized reforms in order to create a more cohesive administrative structure and fostered rapid economic growth.

Marwan ibn al-Hakam ibn Abi al-As ibn Umayya (Arabic: مروان بن الحكم بن أبي العاص بن أمية, romanized: Marwān ibn al-Ḥakam ibn Abī al-ʿĀṣ ibn Umayya; 623 or 626 – April/May 685), commonly known as Marwan I, was the fourth Umayyad caliph, ruling for less than a year in 684–685. He founded the Marwanid ruling house of the Umayyad dynasty, which replaced the Sufyanid house after its collapse in the Second Fitna and remained in power until 750.

During the reign of his cousin, the third Rashidun caliph Uthman (r. 644–656), Marwan took part in a military campaign against the Byzantine Exarchate of Africa (in central North Africa), where he acquired significant war spoils. He also served as Uthman's governor in Fars (southwestern Iran) before becoming the caliph's katib (secretary or scribe). He was wounded fighting the rebel siege of Uthman's house, in which the caliph was slain. In the ensuing civil war between the fourth Rashidun caliph Ali (r. 656–661) and the largely Qurayshite partisans of Aisha, Marwan sided with the latter at the Battle of the Camel. Marwan later served as governor of Medina under his distant kinsman Caliph Mu'awiya I (r. 661–680), founder of the Umayyad Caliphate. During the reign of Mu'awiya's son and successor Yazid I (r. 680–683), Marwan organized the defense of the Umayyad realm in the Hejaz (western Arabia) against the local opposition which included prominent companions as well as Muhammad’s own clan, the Bani Hashim, who revolted under the banner of Muhammad’s grandson, Husayn ibn Ali. After Yazid died in November 683, the Mecca-based rebel and sahabi Abd Allah ibn al-Zubayr declared himself caliph and expelled Marwan, who took refuge in Syria, the center of Umayyad rule. With the death of the last Sufyanid caliph Mu'awiya II in 684, Marwan, encouraged by the ex-governor of Iraq Ubayd Allah ibn Ziyad, volunteered his candidacy for the caliphate during a summit of pro-Umayyad tribes in Jabiya. The tribal nobility, led by Ibn Bahdal of the Banu Kalb, elected Marwan and together they defeated the pro-Zubayrid Qays tribes at the Battle of Marj Rahit in August of that year.