The term Ahlul Bayt refers to the immediate family members of Prophet Muhammad: his daughter Fatima, cousin and son-in-law Ali, and grandchildren Hasan and Husayn. The purity of the Ahlul Bayt is spoken about in the Quran,
“Allah only wishes to remove all uncleanliness from you, O People of the House (Ahlul Bayt), and to purify you completely.” (33:33)
These five members and the nine imams which descend from Husayn are referred to as Ahlul Bayt; and all of them are considered to be infallible.
Near the end of Prophet Muhammad’s life he said, “It is probable that I will be called soon, and I will respond, so I leave behind me, for you, two weighty things: the Book of God [the Quran], and my Ahlul Bayt. Verily, God, the Merciful, the Aware, has informed me that these two will never be separated from each other until they meet me at the fountain in Heaven called Kawthar.”
The Prophet also said, “The parable of my Ahlul Bayt is similar to that of Noah’s ark. Whoever embarks on it will certainly be rescued, but whoever opposes the boarding of it will surely be drowned.”
As a statute, the prophets of God did not ask for any reward in compensation for the pain and suffering that they endured while attempting to guide mankind. In fact, this refusal to accept compensation can be seen as the mark of a prophet. The Quran states,
“Obey those who ask no reward from you and who have themselves received guidance.” (36:21)
However, by the command of God, Prophet Muhammad made one slight exception; although the Prophet refused to accept anything for himself, he was commanded by God to say,
“I do not ask you for any reward except love for my relatives [the Ahlul Bayt].” (42:23)
Imam Ali spoke about Ahlul Bayt as, “We the Ahlul Bayt, possess the doors of wisdom and the light of governance. Be aware that the path of religion is one and its highways are straight. One who follows them achieves and secures the aim and objective; and one who stands away from them goes astray and incurs repentance.” Further he said that the example of the descendants of Prophet Muhammad is like that of stars in the sky, “when one star sets another one rises.”
The Prophet of Islam has stated, “We are lights of the heavens and the earth and the ships of salvation. We are the repositories of knowledge, and toward us is the homecoming of all matters. Through our Mahdi (the final successor to the Prophet) all arguments shall be refuted, and he is the seal of the imams, the deliverer of the Muslim nation (ummah), and the extremity of the light. Happy are those who hold onto our handle and are brought together upon our love.”
 Sahih Muslim, v.2 p.238 and Sahih Tirmithi, v.II p.220.
 Mishkaat al-Masaabih, Ahmad ibn Hanbal, p.523 and Faraid al-Simtayn, v.2 p.242.
 Nahj al-Balagha (The Peak of Eloquence), sermon #120.
 Ibid., sermon #100.
 Sibt ibn al-Jawzi, Tadhkirat al-Khawass, p.138.