Usul al-Kafi
Book 4:
The Book of Divine Proof

Chapter 91
Imam: From cradle to grave

478. 1. A believer asked Imam Muhammad al-Baqir (p): Was Prophet Isa (Jesus) son of Maryam (Mary) (p) a Hujjat for the people of his time when he was in the cradle and talked to people about the innocence of his Mother Maryam (p)?
The Imam (p): Yes. Have you not heard what he said?
The Imam (p) quoted the verses: He (Jesus (p)) said, I am indeed a servant of God, He has given me the Book and has made me a Prophet, and He has made me blessed where ever I be, and has enjoined on me prayer and charity as long as I live (Q, 19:30-31).
The Believer: Was he (Prophet Isa (p)) a Hujjat for Prophet Zakariya (Zachariah) (p) while he was talking to people in his cradle?
The Imam (p): He was a Hujjat for the people and a mercy of God for Maryam (Mary) (p) when he talked and proved the innocence of his mother. At that time he was a Prophet and Hujjat for the people who heard him talking. Then he maintained silence for two years. During these two years Prophet Zakariya (p) was the Hujjat of God for the people. When Prophet Zakariya (p) died, his son Prophet Yahya (John) (p) inherited the Book and wisdom although he was very young. Have you not heard what God, the Mighty, the Glorious, has said: O Yahya (John) (p), take hold of the Book with might, and We gave him wisdom while he was very young (Q, 19:12). When Prophet Isa (Jesus) (p) attained the age of seven he talked about his Prophethood and Apostleship according to the revelation which came to him from God and now Prophet Isa (p) became a Hujjat for Prophet Yahya (John) (p) and all other people. The world does not remain devoid of a Hujjat of God even for a single day. This has held good since Prophet Adam (p) was created and stationed on the earth.
The Believer: May I be a sacrifice for you, was Imam Ali (p) a Hujjat of God and also Hujjat of the Prophet Muhammad (p) for this community during the life-time of the Prophet Muhammad (p)?
The Imam (p): Yes, since the day his Vice-regency was announced (by the Prophet Muhammad (p)) and people were ordered to obey him.
The Believer: Were people bound to obey Imam Ali (p) during the life time of the Prophet Muhammad (p)?
The Imam (p): Yes, but he remained silent and did not dictate (any tenets of religion) during the life-time of the Prophet (p). Obedience to the Prophet (p) was enjoined on Imam Ali (p) and the people during the life-time of the Prophet (p). After the demise of the Prophet Muhammad (p), obedience to Imam Ali (p) was enjoined by God and His Prophet (p) on all people, and Imam Ali (p) possessed knowledge and wisdom.

479. 2. A believer asked Imam Ali ar-Reza (p): Before the birth of Imam Muhammad at-Taqi (p) we used to ask you and you used to say that God will bestow on you a son. Now God has bestowed on you a son and this is a solace for our eyes. If, God forbid, something happens to you, then who will be the authority after you?
The Imam (p) pointed towards Imam Muhammad at-Taqi (p) who was sitting there.
The Believer: May I be a sacrifice for you, he is only three years old.
The Imam (p): This does not matter at all. Prophet Isa (Jesus) (p) was a Hujjat when he was less than three years of age.

480. 5. Imam Muhammad al-Baqir (p) was asked: Whether an Imam can be an active Imam at an age less than seven?
The Imam (p): Yes, even at an age less than five.

481. 6. Imam Ali ar-Reza (p) was asked by a person when he was very young: O my leader, who will be our Imam (p) after you?
The Imam (p): My son (Imam Muhammad at-Taqi (p)). Verily God, the Glorious and the Exalted, conferred Prophethood on Prophet Isa (Jesus) (p) when he was younger than Imam Muhammad at-Taqi (p).

482. 7. A man came from Egypt to visit Imam Muhammad at-Taqi (p) and was surprised to see that the Imam (p) was so young.
The Imam (p) addressed him: Verily, God has acted in respect of Imamate exactly what He has done for Prophethood.
The Imam (p) then quoted three verses: ... And We bestowed upon him wisdom while he was still young (Q, 19:12). (This verse refers to Prophet Yahya (John) (p)) The second verse says: And when he (Prophet Yusuf (Joseph) (p)) attained his full age of maturity, We granted him judgment and learning. Thus do We reward the righteous (Q, 12:22). The third verse says: ...When he attained his full maturity at forty years... (Q, 46:15). After quoting these verses, the Imam (p) said: Wisdom can be given (bestowed by God) at a very young age and even at the age of forty.

483. 8. Imam Muhammad at-Taqi (p) was informed by a believer: Some people do not recognize you as an Imam (p) because of your young age.
The Imam (p): Do they refuse to accept what God, the Mighty, the Glorious said, addressing His Prophet (p): Say thou, this is my way; I call to God on the basis of sure knowledge, I and whoever follows me... (Q, 12:108). And by God no one followed him (as he deserved to be followed) except Imam Ali (p). At that time Imam Ali (p) was nine years old and so am I.