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

Chapter 8
People must obey the Imams

315. 5. Imam Jafar as-Sadiq (p): I am included among the successors and the messengers in true allegiance.

316. 6. Imam Jafar as-Sadiq (p): God, the Mighty, the Glorious, has enjoined upon the people to obey us. For us are the spoils of war and the best of all good things. We are the ones deep-rooted in knowledge and we are those envied ones for whom God said: Or do they envy people for that which God has given them out of His bounty? (Q, 4:54)

317. 9. Imam Jafar as-Sadiq (p) was asked: Do all Imams have equal status as regards their commandments and obedience to them?
The Imam (p): Yes.
318. 10. Imam Ali ar-Reza (p) said to Ishaq Ibn Musa: O Ishaq! I have come to know that people say that we claim all the people to be our slaves. No, I swear by my kinship to the Prophet Muhammad (p), I have never said this, nor have I heard any of my forefathers say so, nor has any report reached me that any of my forefathers have said so. But I will say that people are our slaves in obedience in matters of religion and must accept our mastership in it. Let him who witnesses (this) convey it to those who are absent.

319. 11. Imam Jafar as-Sadiq (p) was asked: What is the best way of attaining nearness to God, the Mighty, the Glorious?
The Imam (p): Refer the verse of the Noble Quran: To obey God and to obey the Prophet (p) and to obey those in authority (the Imam)... (Q, 4:59)
320. 16. Imam Jafar as-Sadiq (p) was asked: Is it our duty to obey the viceregents (of the Prophet Muhammad (p))?
Imam Jafar as-Sadiq (p): Yes, it is they, about whom God, the Mighty, the Glorious, said: O You who believe, obey God and obey His Messenger and those who are in authority among you…(Q, 4:59) and it is they, about whom God, the Mighty, the Glorious said: Verily, your (real) guardians are God and His Messengers and those believers who offer prayers and pay the prescribed poor-due (Zakat) while they bow (Q, 5:55).