Imam Sadiq (peace be upon him): A person asked Imam Sadiq (peace be upon him): "...O son of the Messenger of Allah (peace be upon him and his family), tell me who is the ummah of Muhammad (peace be upon him and his family)? Is only the household of the Prophet (peace be upon him and his family) meant?" He said: "Yes." He said: "That is, all Muslims and all those who believed in him and affirmed him are not meant?" Imam Sadiq (peace be upon him) said: "Allah the Mighty and Majestic said in another place [of the Quran]: 'You are the best ummah brought forth for mankind' (Al-i Imran/110). And if Allah meant all Muslims, that they are the best ummah whom Allah has appointed for the guidance of people, then who are the 'people' (nas) to whom all Muslims have been sent? Never — Allah did not intend that the meaning of 'nas' be the low and base people; rather what Allah meant by 'ummah' is the group amongst whom Muhammad (peace be upon him and his family) was raised." The questioner asked: "But no one was with him except Ali (peace be upon him)?" Imam Sadiq (peace be upon him) said: "Along with Ali (peace be upon him), Fatimah (peace be upon her), Hasan (peace be upon him) and Husayn (peace be upon him) are also included in this verse, and they are the ones from whom Allah has removed impurity and purified them thoroughly; and they are the very Ashab al-Kisa (People of the Cloak) to whose purity the Quran bears witness. Moreover, the Messenger of Allah (peace be upon him and his family) himself was a single ummah, because Allah said: إِنَّ إِبْراهِیمَ کانَ أُمَّةً قانِتاً لِلَّهِ حَنِیفاً [Surely Ibrahim was an ummah, obedient to Allah, upright]. With these attributes, Ibrahim (peace be upon him) alone was an ummah, until in the time of his old age Ismail and Ishaq (peace be upon them) were granted to him, and in this manner He placed prophethood in the heavenly Book among the descendants of those two. The Messenger of Allah (peace be upon him and his family) too was at first [a single, unified ummah alone], until Ali (peace be upon him) and Fatimah (peace be upon her) were granted to him, and with Hasan and Husayn (peace be upon them) He multiplied them, just as He multiplied Ibrahim (peace be upon him) with Ishaq and Ismail (peace be upon them)."