From the Shia perspective, based on authentic narrations, the “Itrah” mentioned by the Messenger of God (peace be upon him and his family) in the Hadith al-Thaqalayn are Imam Ali (peace be upon him), Lady Fatimah (peace be upon her), Imam al-Hasan (peace be upon him), Imam al-Hussain (peace be upon him), and the nine Imams from the progeny of Imam Hussain (peace be upon him), the last of whom is Imam al-Mahdi (may Allah hasten his reappearance).
The Itrah of the Chosen Messenger
Allamah al-Majlisi, in his commentary on the phrase “and the progeny of the Chosen One of the Lord of the Worlds” from Ziyarat al-Jamiah al-Kabirah, states,
“‘Itrah in language signifies fragrance, or a necklace filled with musk and amber. It also denotes close kinship. In the authentic narration of Hadith al-Thaqalayn, the Messenger of God (peace be upon him and his family) declared:
‘I am leaving among you two precious legacies: the Book of God and my Itrah—my Ahl al-Bayt.’”
The Explanation of Imam Ali (peace be upon him)
Imam Jafar al-Sadiq (peace be upon him) narrated from his forefathers that the Commander of the Faithful (peace be upon him) was asked about the saying of the Prophet (peace be upon him and his family):
“I leave among you the two weighty things—the Book of God and my Itrah.”
The Imam was asked, “Who are the Itrah of the Messenger of God?”
He replied:“I am, along with al-Hasan, al-Hussain, and the nine Imams from the descendants of al-Hussain—the ninth of them is al-Mahdi. They shall never be separated from the Book of God, nor will the Book of God be separated from them, until they meet the Messenger of God at the Fountain (of Kawthar) on the Day of Resurrection.”
The Testimony of the Prophet (peace be upon him and his family)
Imam al-Sadiq (peace be upon him) also narrated that the Messenger of God (peace be upon him and his family) said,
“I am leaving among you two precious things: the Book of God and my Itrah, my Ahl al-Bayt. The two shall never be separated until they return to me at the Fountain.”
At that moment, Jabir ibn ‘Abdullah al-Ansari asked, “O Messenger of God, who are your Itrah?”
The Prophet replied,
“Ali, al-Hasan, al-Hussain, and the Imams from the descendants of al-Hussain, until the Day of Resurrection.”
The First and the Last of the Imams
Shaikh al-Saduq, after citing these narrations, commented:
“The Itrah are Ali ibn Abi Talib (peace be upon him) and his progeny from Fatimah (peace be upon her)—the descendants of the Messenger of God (peace be upon him and his family)—those whom Allah, through His Prophet, explicitly designated as the Twelve Imams: the first being the Commander of the Faithful, and the last being al-Qaim (peace be upon him).”
The Debate of Imam al-Ridha (peace be upon him) with al-Mamun
In a public debate arranged by the Abbasid caliph al-Mamun, with the scholars of Iraq and Khurasan present, he asked Imam Ali ibn Musa al-Ridha (peace be upon him),
“Who are the purified members of the Prophet’s family?”
The Imam replied,“They are those about whom Almighty God said:
‘Indeed, Allah desires to remove impurity from you, O People of the Household, and to purify you thoroughly.’ (Quran)
That is, He purified them from every vice, error, and sin.”
The Imam continued,
“They are the ones about whom the Messenger of God said: ‘I leave among you two precious things — the Book of God and my Itrah. the people of my household. They shall never part until they return to me at the Fountain.
So consider well how you treat them and how you follow them. Do not presume to teach them, for their knowledge surpasses yours.”
The scholars present then asked,
“Are the Itra identical with the Prophet’s family (Āl Muhammad)?”
The Imam answered, “Yes, they are his family.”
When the scholars claimed that all the Prophet’s followers are his Āl, Imam al-Ridha (peace be upon him) refuted them by saying:
“Tell me—is charity (zakat) lawful for the Āl Muhammad?”
They answered, “No.”
He asked, “And is charity lawful for the Muslim community (Ummah)?”
They said, “Yes.”
The Imam concluded, “This is the distinction between the Āl and the Ummah.”
The Descendants of the Final Prophet
Opponents, too, have transmitted reports confirming that the Prophet (peace be upon him and his family) said,
“God has made the offspring of every Prophet to come through his own loins, but He made my offspring to come through the loins of Ali.”
The Prophet also said,
“O Fatimah! God did not send any prophet except that his progeny came from his own line. Yet He has decreed that my progeny shall come through the line of Ali. Were it not for Ali, my lineage would not continue on earth.”
The Ahl al-Bayt: One Light and One Spirit
The Messenger of God (peace be upon him and his family) once asked Lady Fatimah (peace be upon her):
“What is the best state for a woman?”
She replied,
“That she should not see a man, nor should a man sees her.”
The Prophet embraced her and recited:
‘They are a progeny, one from another.’ (Quran)
Allamah al-Majlisi commented on the phrase “Your souls, your light, and your essence are one” from Ziyarat al-Jamiah al-Kabirah:
“This means that the souls of the Imams and Lady Fatimah (peace be upon her) are one soul — created from the light of the Messenger of God (peace be upon him and his family). Their knowledge and perfections are one illumination. They are all of a single essence and nature, pure from any defilement or sin, as God has said: ‘A progeny, one from another.’”
The Debate with Harun al-Rashid
Imam Musa ibn Jafar al-Kadhim (peace be upon him) recounted his debate with Harun al-Rashid, who questioned how the descendants of Fatimah (peace be upon her) could be called the offspring of the Prophet (peace be upon him and his family). The Imam proved through the Quran—citing verses about Prophet Jesus (peace be upon him), who had no father, and the Verse of Mubahalah (Quran)—that descent through a daughter is legitimate in divine reckoning.
He said,
“No one claims that the Prophet, during the Mubahalah, took anyone with him except Ali, Fatimah, Hasan, and Hussain (peace be upon them). Thus, ‘our sons’ refers to Hasan and Hussain, ‘our women’ to Fatimah, and ‘ourselves’ to Ali.”
When Harun acknowledged the strength of his argument, he said, “Excellent, O Musa.”
Thus, the reasoning of Imam Musa al-Kadhim (peace be upon him) conclusively establishes that all the descendants of Lady Fatimah (peace be upon her)—the noble Sadat Fatimiyah—are the true progeny of the Messenger of God (peace be upon him and his family).
