Imam Ali (as): Verily Islam is submission, and submission is conviction, and conviction is certification of something, and certification is attestation, and attestation of something is fulfilment of it, and fulfilment is the performance of required acts. A believer does not take his religion from his own personal opinion, rather he takes his religion from that which has come from his Lord. A believer's conviction can be seen in his actions. al-Kāfī