Conviction is the constant believing in the principles of the religion. Such believing should conform to the reality and not be shaken by suspicions. If it does not, it is then compound ignorance.
The Islamic Sharia has taken a special notice of conviction and showered people of conviction with glorious items of praise:
Amir ul-Mu’minin (a) used to say: “No one can find the true taste of faith before he believes that whatever befell him would never miss him and whatever missed him would never befall him. The real source of harm and benefit in only Allah.”
Imam as-Sadiq (a) said: “Faith is preferable to being Muslim. Conviction is preferable to faith. In fact, there is nothing more powerful than conviction.”
“The little permanent deed with conviction is favorable in the sight of Allah to the many deeds that are lacking conviction.”
“To avoid pleasing anyone and discontenting Allah and reproaching anyone for something that Allah has not given to you—these are parts of the trueness of Muslim’s conviction. The sustenance cannot be obtained through (any sort of) niggardliness and will not be ceased when someone hates it. If you escape your decided share of sustenance in the same way as you escape death, it will surely catch you in the same way as death will inevitably catch you. Out of His justice and equality, Allah has made pleasure and rest lie in conviction and content, and has made care and grief lie in suspect and dissatisfaction.”
Once, Imam ar-Rida (a) was asked to identify the best of two men one of whom says only the truth, but he commits wrongdoings, consume wines, and perpetrates the grand sins, while the other is less in conviction but he does not commit such evildoings. The Imam said: “The first one is just like a man who sleeps on the right course; as soon as he is awaken, he will take it. The other is like a person who sleeps on the wrong course; when he is awaken, he cannot realize the right course to take.”
Imam as-Sadiq narrated that the Prophet (s) once, noticed a young man, in the mosque just after the Fajr prayer, nodding his head with his face pale, his body thin, and his eyes sunken in his head. ‘How is your morning?’ the Prophet asked the young man. ‘God’s Messenger,’ answered the man, ‘I begin this morning with full conviction.’
The Prophet (s) was admired by this answer; hence, he said, ‘There is a proof for every conviction. What is the proof of yours?’
The young man said, ‘God’s Messenger, my conviction is the reason of my grief, sleeplessness, and thirst in midday. Hence, I disdain this world along with its pleasures so completely, as if the Throne of my Lord is prepared for the judgment, all people, including I myself, are gathered there for interrogation, and as if people of Paradise are there enjoying the bliss and introducing themselves to each other and leaning on the sofas, and as if people of Hell are there tormented and lined up, and now I can hear the sound of fire in my hearings.’
The Prophet (s) said to his companions, ‘Surely, Allah has illuminated the heart of this man with faith.’ He (s) then asked him to keep on such faith and conviction. The young man asked the Prophet to pray to God for martyrdom, and the Prophet did.
Not before long time, that young man participated in one of the Prophet’s campaigns and was martyred.