There is no need for it. However, it occurs through iman (faith), intellect, maʿrifa (gnosis, experiential knowledge of God), and the servant's proper management of both the outward and inward aspects of his state. Subsequently, one understands ṣidq (truthfulness), and also understands its opposite, lying. Just as one understands good, one also understands its opposite, evil. One strives to establish ṣidq and to eliminate its opposite. The essence is distinguished from the branch.
One's engagement in understanding and manifesting ṣidq is from the perspective of the essence. Likewise, one is engaged in eliminating its opposite from this perspective. The essence precedes the branches (the root or foundation comes before the offshoots). If the servant continues to engage with the branches based on the essence, as long as the essence persists, his engagement does not cease. Whenever a branch disappears, another branch comes to replace it. (Adāb, 107)
Yaqīn (certainty) is according to a person's iman. (Adāb, 185)
When Abū Yazīd Bisṭāmī was asked what tawhid (the oneness of God) is, he replied: "It is yaqīn." When asked, "What is yaqīn?" he said: "It is to know that the movements and stillnesses of people are the act of Allah, and that no one can be a partner to Him in His acts." When you recognize your Lord and your Lord settles within you, it means you have found Him. Its meaning is this: You understand that Allah is unique in His acts, having no partner, and that no one can perform His acts.
Yaqīn is mukāshafa (unveiling). There are three types of mukāshafa: The first is the unveiling seen with the eye on the Day of Qiyāma (Resurrection); the second is the discovery by the hearts, through yaqīn, of the realities of iman in a manner that cannot be described or defined; the third is the unveiling of miracles to non-prophets through karāma (a saintly wonder) and answered supplications, just as miracles are manifested to prophets through qudra (divine power). (Lumaʿ, 102)
The people of yaqīn (those endowed with certainty) are of three degrees: The first is the asāghir, that is, the yaqīn of the murīd (aspirants, disciples) and the common people. One of the Sufis described it thus: The first degree of the maqām (spiritual station) of yaqīn is to trust in what is in Allah's hand and not to covet what is in the hands of people. When Junayd was asked about the maqām of yaqīn, he replied: "Yaqīn is the removal of doubt." Abū Yaʿqūb (al-Sūsī) said: "When the servant is content (riḍā) with what Allah has apportioned to him, his yaqīn in that matter has reached perfection (kamāl)."
When Ruwaym Aḥmad was asked about yaqīn, he replied: "It is for the qalb (the heart) to realize the meaning upon which it stands."
The second degree of yaqīn is the awsāṭ, that is, the yaqīn of the khawāṣṣ (the elect). Their yaqīn is expressed in Ibn ʿAṭāʾ's answer to the question, "What is yaqīn?": It is the continual struggle according to the persistence of moments, that is, to constantly oppose the nafs (the lower self) in matters of iman...
The third degree of yaqīn is the akābir, that is, the yaqīn of the elite of the elect. ʿAmr ʿUthmān al-Makkī expressed this yaqīn as follows: "It is the realization of Allah's affirmation with all His attributes." The final point of yaqīn is the attachment of the hearts to Allah through yaqīn that arises in the hearts by means of actions that bring about inspiration (ilhām). (Lumaʿ, 102)
Yaqīn is the foundation of all ḥāl (spiritual states). All states culminate in it. It is the end of the states, the inner reality (bāṭin) of all states. All states are the outward manifestation (ẓāhir) of yaqīn. The ultimate end of yaqīn is to realize the affirmation of the unseen (ghayb) by removing all traces of doubt and suspicion. The result of yaqīn is to rejoice, to taste the sweetness of munājāt (intimate supplication), and to reach a purity that allows the qalb to gaze upon Allah Most High by witnessing the realities of yaqīn, after all objections tainted by motives and suspicions are removed. (Lumaʿ, 103)
Junayd said: "Yaqīn is the removal of doubts."
(Abū Ḥusayn) al-Nūrī also said: "Yaqīn is witnessing (mushāhada)."
Ibn ʿAṭāʾ said: "Yaqīn is the absence of any objection whatsoever."
Dhū al-Nūn also said: "Everything the eye sees is knowledge, everything the heart knows is yaqīn." Another said: "Yaqīn is the eye of the heart."
ʿAbdullāh said: "Yaqīn is the union of the intervals and the removal of what lies between them." The statement of Ḥāriṯa, "It is as if I am looking at the Throne of my Lord," indicates that his vision has united with the unseen, and the veils between him and the unseen have been lifted.
Sahl also said: "Yaqīn is mukāshafa (unveiling)." Just as he said in this regard: "The lifting of the veils would not increase my yaqīn." (Taʿarruf, 73)
One who possesses the knowledge of yaqīn does not fall into doubt in the sense used by the scholars, nor in the absolute sense. Since it does not occur in the scriptural texts, the term yaqīn is not used as an attribute of Allah. ʿIlm al-yaqīn (the knowledge of certainty), ʿayn al-yaqīn (the eye of certainty), and ḥaqq al-yaqīn (the reality of certainty) are all, in fact, yaqīn itself... (Qushayrī, 47)
Even the least amount (the minimum) of yaqīn that reaches the qalb fills the heart with light. (Yaqīn) removes all doubts from the qalb, and through it, the heart is filled with shukr (gratitude) and fear of Allah. (Qushayrī, 90)
Yaqīn arises from the increase and realization of iman. Sahl said: "Yaqīn is one of the branches of iman; it is something beyond mere affirmation."
Someone said: "Yaqīn is the knowledge deposited in hearts." This person indicated that yaqīn is not acquired (kasbī) but is bestowed (wahbī), that is, it comes from Allah and is not attained through effort.
Sahl said: "The beginning of yaqīn is mukāshafa (unveiling)." For this reason, one of the early generations said: "If the veil were lifted, my yaqīn would not increase." After mukāshafa comes muʿāyana (direct vision), and then mushāhada (witnessing).
ʿAbdullāh Ḥafīf said: "Yaqīn is the realization of the secrets related to the rulings of the unseen (ghayb)."
Abū Bakr Ṭāhir said: "Knowledge can be subject to doubts, but in yaqīn there is no doubt." By this, he indicated the difference between acquired knowledge and self-evident (wahbī, divinely sourced) knowledge. The knowledge of the Sufis at the beginning is acquired, but in the end, it becomes self-evident.
Dhū al-Nūn al-Miṣrī said: "Yaqīn is the shortening of hopes (kasr al-amal); kasr al-amal leads to zuhd (asceticism); zuhd leads to ḥikma (wisdom), and wisdom leads to reflection on the outcome of affairs." (Qushayrī, 90)
When Sari al-Saqaṭī was asked, "What is yaqīn?" he replied: "Yaqīn is to remain calm so that, when inspirations (wārid) circulate in your breast, you are certain that acting in that moment will not benefit you, nor will it change what has been decreed for you."
Abū Bakr Warrāq said: "Yaqīn is of three kinds: yaqīn related to report (khabar), yaqīn related to indication (dalāla), and yaqīn related to witnessing (mushāhada)." (Qushayrī, 91)
Knowledge about which there is no yaqīn regarding its soundness is not (true) knowledge... (Hujwīrī, 464)
Allah Most High has said: "For the possessors of yaqīn there are signs on the earth." Yaqīn is the mount of the one who enters this path, and it is the end of the degrees of the common people. It is also said to be the first step of the elect.
There are three degrees of yaqīn. The first degree is ʿilm al-yaqīn, which is to accept everything that appears from the Truth (al-Ḥaqq) and everything that is absent concerning the Truth, and to be aware of everything that subsists by the Truth.
The second degree is ʿayn al-yaqīn, which is the realization (istidrāk) of hidden matters...