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

Chapter 59
The legacy of one Imam to another

345. 1. Imam Muhammad al-Baqir (p) was requested to explain the meaning of the verse: If you do not know then ask those who are deeply rooted in knowledge. (Q, 16:43)
The Imam (p) quoting the Prophet Muhammad (p): I am the repository of knowledge and the Imams are the exponents of knowledge.
The Imam (p) also quoted the verse: Surely this (Quran) is a Message for you and for your people and you will be questioned (about it). (Q, 43:44)
The Imam (p): We are the people of the Prophet Muhammad (p) and we are the people who should be asked (regarding all matters of religion).

412. 1. Imam Muhammad al-Baqir (p) was asked by Burayd al-Ijli about the words of God, to whom belong Might and Majesty: God commands you to convey the trusts to their owners; and when you judge between the people, you judge with justice… (Q, 4:58).
The Imam (p): It is about us, that means the preceding Imam should convey the Books, the Knowledge and the Arms to the Imam who comes after him. And when you judge between the people, you judge with justice, which is in your hands. Then He tells the people: O Believers, obey God, and obey the Messenger and those in authority among you… (Q, 4:59) By those in authority, He means ‘us’ exclusively. He has commanded all believers till the Day of Resurrection to obey us. If there is dispute in any matter, refer it to God, and the Prophet Muhammad (p) and those in authority among you. This is how it was sent down. Then, how could God, to whom belong Might and Majesty, order them to obey those in authority and allow strife among them? Surely, this was said about those who have been trusted upon; it was said about them: Obey God, and obey the Messenger and those in authority amongst you… (Q, 4:59)
413. 2. Imam Ali ar-Reza (p) was requested to explain the meaning of the verse: God commands you to make over the trust to those to whom they are due… (Q, 4:58)
The Imam (p): They are Imams from the progeny of Prophet Muhammad (p). An Imam is commanded by God to transfer the trust to the Imam after him, and not to include others in this privilege.