"The believer enriches his knowledge with patience; he takes part in a gathering only to learn; he remains silent and listens so as to escape harm; he speaks so as to comprehend. He does not divulge that which has been placed in his trust even to his confidants and does not refrain from bearing witness in favor of his adversaries. He does not undertake a righteous act in order to impress, nor does he avoid undertaking a righteous act out of shame. When admired, he is weary of that which is said about him, and he asks God for forgiveness on account of that which his admirers do not know about him. He is not fooled by that which is said about him by those who are ignorant of him and is wary of the reckoning [of his actions] by Him Who knows him well [namely, God]."
--Imam Ali ibn al-Husayn Sayyid al-Abedin
قال الامام علي بن الحسين سيد العابدين عليه و علی آبائه الاف التحية و الثناء
المؤمن خلط علمه بالحلم يجلس ليعلم و ينصت ليسلم و ينظق ليفهم لا يحدث امانته الاصدقاء و لا يکتم شهادته الاعداء و لا يفعل شیئا من الحق رياء و لا يترکه حياء ان زکي خاف مما يقولون و يستغفر الله مما لا يعلمون لا يغره قول من جهله و يخشی احصاء من قد علمه
In light of this hadith, the signs of a true believer are as follows.
1) His knowledge is supplemented with patience. There are a few possible meanings that can be inferred here. One is that although he knows what the right course of action is, he is patient. He is not infuriated if others do the wrong thing; rather, he tries to comply with the truth, but is lenient and forgiving if others fail to comply with that which he knows to be right. This is a very important trait. Oftentimes, we are harsh in respect to others, but lenient in respect to ourselves. It should be the other way around.
2) When he attends a gathering, it is not to impress others by his knowledge or piety; it is not to prove anything to anyone else; it is only that he may learn. The believer is ever attentive, never complacent.
3) When there is an argument or an occasion for misunderstanding and, consequently, the flaring of emotions, the believer remains silent, so as not to jump to unwarranted conclusions in the heat of the moment. He remains silent, listens carefully, keeps his composure, ponders the situation sufficiently and only then takes action.
This is one instance of how remaining silent can spare one a great many headache. There are many other instances that fit this description. The important point to remember is that we must be sparing in our speech, more eager to listen than to speak, and speak only when we have given the matter at hand sufficient thought. A case in point in this relation is the very illuminating habit that one of the great contemporary scholars, Ayatullah Misbah Yazdi (may God prolong and bless his life), maintains. When he is asked a question, he without fail remains silent for a few moments, noticeably thinking about what answer to give. He does not open his mouth instantaneously, as most of us are apt to (speaking for myself!). He lets the question sink in and gives it sufficient thought so as to offer the best answer he can possibly offer.
4) When the believer speaks, he speaks in order to add to his knowledge. This is especially true when there is a debate. When gripped by the momentum of a debate, most people tend to speak out of an instinctual urge to prove their point of view, to press onward in reinforcing the position one has put forth. The believer, however, speaks so as to get a better understanding of the question, and he is not ashamed to retract his initial claim if he realizes that it was wrong.
This is a very critical point relative to one's moral and spiritual wellbeing. It is especially important for those engaged in the study of theology and the divinities. (I can speak from personal experience.) It is not an overstatement to say that many students of religion unfortunately are inclined to engage in debates for debate's sake and for demonstrating their superior polemical prowess. God protect us against such evil inclinations and impulses.
5) The believer is excruciatingly careful to safeguard those secrets to which he has been made privy--whether they be personal secrets or social secrets. There are multiple reports in the corpus of Shia tradition that relate the Imams' cursing by name some of their followers for their failure in bearing a secret. Close companions are cursed by the Imams for divulging a secret about the Shia fiath they were supposed to protect.
It is an unpardonable sin to treat the secrets we know about others in a carefree manner. According to the report at hand, we must keep them a secret even from our closest friends in whom we have absolute trust.
6) The believer is fair, not to his friends, but to his adversaries. To his friends, the believer must be self-sacrificing, loving, caring, and solicitous. That, however, is not enough to qualify one as a legitimate believer. To be a true believer, we must be fair to our enemies and adversaries.
7) The believer is careful not to do anything for the sake of impressing others. At first, this may seem to be stating the obvious; yet, in action it is extremely difficult to practice. So difficult is it that the late Ayatullah Khoshvaqt (may God bless his soul) would instruct his students to refrain from performing the supererogatory prayers in the presence of others, for fear that there may be latent in the depths of our hearts an urge to display our acts of worship and piety. He would tell his students that, if possible, they should perform the supererogatory prayers where even their spouses would not see them. And this was not a hypersensitive concern. A very credible report in the corpus of Shia tradition, which the late Imam Khomeini (may God bless his soul and enable us to follow in his footsteps) cites in his Forty Hadiths, likens the difficulty of detecting riya' (the term we have translated here as the impulse to impress others but which is commonly translated as "ostentation") to the almost impossible act of noticing a black ant walking on a black rock in a pitch-dark night. The spiritual stakes are very high. Thus, the believer performs acts of devotion in secret, where this is possible, and when some act of devotion or other manifestation of righteousness must be performed in public, he is careful to do it in a manner that is least prone to occasion the very spiritually destructive sin of riya'.
8) The believer is genuinely and openly proud of his faith. Where others may view his faith with disdain, he is more intent on carrying out the actions that his faith demands. This can take many shapes and forms. When travelling, for instance, we must be careful to perform our prayers on time. Of course, this does not mean that we should ignore the governing rules and regulations. We must abide by the established rules and regulations but also proudly practice our faith. There is nothing wrong with praying in the airport where others see us. There is nothing wrong with making wudu in public restrooms under the curious and possibly even disapproving gaze of non-Muslims.
This is one manifestation. On the other hand, if our faith requires us to perform a certain action that many believers view as opposed to our faith, we must not shy away. You may have heard the report that relates that one day on his way back from his orchards, Imam Baqir, who was heavyset and so was walking with the help of his servants, being exhausted after a day's hard work, encountered a shabby Sufi. The Sufi mockingly inquired why the Imam bothered laboring in orchards instead of immersing himself in prayer and worship. The Imam replied that work was a very important aspect of religious life.
9) Last but not least, the true believer loathes being complimented. To feign humility and act distressed by a compliment is hypocrisy, not sincerity. Sincerity is to genuinely feel sickened when we are admired, to feel ashamed before God, our Lord, for knowing that what we are being credited with is not necessarily a right cause for admiration and that the sins and errors that we know ourselves to suffer from are much greater in comparison to the apparent virtue for which we are being lauded.
We ask God and sincerely pray to him that he enable us to adopt these characteristics and traits that Imam Sajjad in the report at hand specifies as identifying the true believer. Amen.
 Shaykh Saduq, al-Amali, 6th edition (Tehran: Ketabchi, 1376 AH(solar)), pp. 493-494.