Banū Hāshim was a clan in the Quraish tribe. Muhammad, was a member of this clan; his great-grandfather was Hashim, for whom the clan is named. Members of this clan are referred to in English and the Anglicised version of their name as Hashemites, or carry the family name Hashemi or Abbasi. Descendants of Muhammad usually carry the surname Hussaini or its variations (see Hussein el-Husseini, Ali al-Husayni al-Sistani and Ali Hoseyni Khamenei), or the titles Sayyid or Sharif. Amongst pre-Islamic Arabs people classified themselves according to their Confederation, their tribe, their clan, and then their house/family. There were two Tribal Cofederations; the Adnani (Northern, but not necessarily geographically), and the Qahtani (Southern, and again not geo-specific). Banu Hashim is one of the clans of the Quraysh tribe, of the Adnani confederation. It derives its name from Hashim, the great-grandfather of Muhammad, and along with the Banu Abd Shams, Banu Al-Muttalib, and Banu Nawfal clans comprises the Banu Abd al-Manaf section of the Quraysh.
The house of Abd'al-Muttalib of Banu Hashim of Quraysh comprised a form of nobility in pre-Islamic Makkah, based upon their hereditary duty to act as stewards and caretakers of the pilgrims coming to Makkah to worship at the Kaabah. This was the sacred shrine in that city, which in Islamic tradition was built by the Prophet Ibrahim (Abraham) and his first-born son and heir Ismaeel (Ishmail), which had come to be occupied by some hundreds of idols. The idols represented many different tribes and as a result Makkah became a centre of pilgrimage, and the Kaabah's environs were an inviolable sanctuary. This pilgrimage traffic added considerably to the wealth of the merchants of Makkah, which also benefitted from its position astride the caravan routes from Yemen (Arabia Felix) up to the Mediterranean markets.
It was into the house Abd'al-Muttalib of Banu Hashim of Quraysh that Muhammad was born in the year 570 C.E. From 610 C.E. his mission to call people to the worship of the One God set him at odds with the established powers in Makkah. His membership of the 'top house, of the top clan' (in terms of prestige, though not power) was a factor in keeping him safe from assassination during the early years of his mission, as a number of his uncles would not countenance any such insult to our clan honour.
In the year 622 C.E. the Muslim community of Makkah made Hijrah/emigrated to the city of Yathrib, which subsequently became known as Madinah, to avoid the often murderous persecution of the pagans of Makkah.
With the conquest of Mecca in 630, the city was captured by the army of Islam. The Kaabah was cleansed of idols and became the centre of pilgrimage for Muslims. (It is forbidden to non-Muslims to enter an area designated around the city of Makkah).
Though Muhammad had a number of wives few of his children lived long enough to produce any ongoing lines of descent. The two major lines of descent are those of his two grandsons, Al-Hasan and Al-Husayn, born of the union of his daughter Fatima and his cousin/son-in-law Ali. Muhammad besought the mercy of the Muslims upon his beloved grandsons, thus their descendants have become a form of spiritual aristocracy amongst many, though not all, Muslims. The descendants of the Prophets grandsons are known by the titles of Sayed (Sayyid, Syed, etc.), or Sharif/Sherif.
It is to be noted though that over the centuries a great many 'false' Sayedi/Sharifi lines of descent have developed. These have often arisen not through deceit upon their part as much as through the obfuscation of genealogical identity over largely unrecorded centuries. Two known clusters of 'false Sayeds' are: the so-called 'Sayeds of Sindh' in modern Pakistan, descendants of the Ansar (helpers) of a Sayedi/Sharifi refugee from Madinah whose line died out early on thus creating the impression amongst the descendants of those who sheltered him that they were Ahl an'Naas('of the blood') and the 'Talukdari Sayeds' of Hyderabad Deccan in Southern India, the descendants of Muhammad an adopted son of the Prophet Muhammad and therefore also not 'of the blood'.
To try to resolve the confusion surrounding the descendants of Muhammad, the Ottoman Caliphs during the 19th Century C.E. attempted to replicate the Almanach de Gotha (the tome listing the Noble houses of Europe) to show known and verifiable lines of descent. Although not 100% complete in its scope (some lines might have been excluded due to lack of proof, although no false lines are included) the resulting 'Kitab al-Ashraf (Book of the Sharifs), kept at the Topkapi Palace (Museum) in Istanbul is one of the best sources of evidence of descent from the Prophet Muhammad.
The Alid (the term given to the descendants of Muhammad via his daughter Fatima and Ali) lines of descent produced many once, current (and future) reigning dynasties across the Islamic imperium, amongst these stand:
• the Zaydid Imams of Tabaristan (Al-Hasan of Banu Hashim of Nishapur);
• the Jafaari Sharifs of Sus/Saadian Sultans of Morocco (16-17ty Centuries C.E);
• the Al-Aoute Sharifs, who reign in Morocco currently;
• the former Sharifs of Makkah, who now rule Jordan (and used to rule the Hejaz and Iraq also);
• the Idrissid Sharifs, who ruled parts of North Afrika from Fez (8th-10th Centuries C.E);
• the Hammudids of Spain;
• the Daoudi Sulaymanids of Yemen;
• the Ibrahimi Imams of Yemen;
• the Maghrabi Sulaymanids;