Kashf

Kashf () "unveiling" is a Sufi concept dealing with knowledge of the heart rather than of the intellect. Kashf describes the state of experiencing a personal divine revelation after ascending through spiritual struggles, and uncovering the heart (a spiritual faculty) in order to allow divine truths to pour into it. Kashf is etymologically related to "mukashafa" “disclosure”/ “divine irradiation of the essence”, which connotes "gain[ing] familiarity with things unseen behind the veils". For those who have purified their hearts, and who come to know the Divine Names and Attributes to the fullest of their individual capacities, the veils in front of the purely spiritual realms are opened slightly, and they begin to gain familiarity with the unseen. In Sufism, an even further revelatory capacity exists by which the Divine mysteries become readily apparent to the seeker through the light of knowledge of God. This is called "tajalli" "manifestation".
Veil References in Islamic Literature.
Two passages in the Qur'an serve as the most solid basis for elaboration on the Sufi concept of kashf:
The verb “kashafa,” but never the noun “kashf” occurs in the Qur'an a variety of times in the sense of either “to uncover” (a part of the body) or “to take away” (misfortune, danger).
Hadith of the Veils
One hadith holds particular significance for the concept of "kashf":
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"Between God (mighty and sublime) and creation are "70,000 veils". The nearest of creatures to God (mighty and sublime) are Gabriel, Michael, and Raphael, and between them and Him are four veils: a veil of fire, a veil of darkness, a veil of cloud, and a veil of water."
This Hadith is quoted somewhat differently by "Ibn Majah" as follows:
“God has seventy thousand veils of light and darkness; if He were to remove them, the radiant splendors of His Face would burn up whoever (or ‘whatever creature’) was reached by His Gaze.” 
It is said that Ali ibn Abi Talib, cousin to the Prophet Muhammad, prayed a prayer that included this excerpt during the month of Sha'baan:
My Lord, grant me complete severance of my relations with everything else and total submission to You. Enlighten the eyes of our hearts with the light of their looking at You to the extent that they penetrate the veils of light and reach the Source of Grandeur, and let our souls get suspended by the glory of Your sanctity.
Sufi Scholars on Kashf.
Al-Kushayri expands on al-Kalabadhi’s proposal that "tajalli" (manifestation) of “the essence” of the Divine is called "mukashafa". He then illustrates three stages in progression towards understanding the Real:
Al-Ghazali—This Sufi scholar discusses the concept of kashf, not purely in its mystical sense, but also with respect to theology in general. In conjunction with Al-Kushayri, Al-Ghazali links kashf with intuition. For Al-Ghazali, mukashafa has a dual sense:
Since, for Al-Ghazali, "kashf" is linked to intuition, he describes "mukashafa" as the certain knowledge of the unseen discovered by the “science of the saints”. Thus, "kashf" is considered “a light,” that is freely bestowed upon the purified worshipper through the grace of God, yet also yields sure intuitive knowledge for the worshipper upon whom it is bestowed.
Ibn Arabi—This Sufi mystic indicates the necessity for “divine unveiling” ("kashf") as the means by which to understand the universality of the reality of realities (i.e. the universality of God’s oneness). In "fana" (self-annihilation), the individual ego passes away and divine self-manifestation occurs. This self-manifestation is eternal (as it comes from God), but it must be continually reenacted by the human in time. Therefore, the human becomes a pure receptor required for pure consciousness to be realized. The human is a sort of "barzakh" or intermediary between divinity and elementality, between spirit and matter, and open to the experience of "kashf".
Ali Hujwiri—The author of the Persian Sufi text "Kashf ul Mahjoob" (Revelation of the Veiled) Hujwiri argues, along with Al-Kushayri that very few "real" Sufis exist anymore in his time; rather, there are a large number of “false pretenders” which he calls "mustaswif"—“the would-be Sufi”. In his text, Hujwiri describes the “veils which should be lifted” in order to purify one's heart and really pursue Sufism. Hujwiri argues for the importance of “morals” over “formal practice” in Sufism. He was the first to directly address the problematic diversity in Muslim belief during his time. In "Kashf ul Mahjoob", he describes various Sufi approaches to theoretical ideas, linking them to particular key Sufi figures.
"Kashf" and Shi’ism.
In Shi’ism, the spiritual experience of "kashf" is treated as a theological rather than purely mystical dimension.
Controversy in the Muslim World.
The concept of "kashf" remains controversial in the Muslim world because it indicates the ability to “know” the unknowable. According to the Qur'an, Muslims are required to believe in the unseen (namely Allah), but knowledge of the unseen is a power that should belong solely to God. But it does not contradict the Qur'an because only God has knowledge of the unseen and if someone else other than God has that knowledge, then it's only because it was given to them by God.
Sufis further would argue that “the only guide to God is God Himself”. They do believe that every genuine worshipper has the capability to experience unveiling (personal revelation), but that this personal revelation occurs by the grace of God. Some say, if a worshipper fails to experience unveiling, "it indicates that that person is pursuing Sufism for a reason other than the love of God alone." - However this in fact, incorrect. As devout Sufis believe that every individual's experience in sufism is different, similarly to how different people have the ability to see different things, therefore one can confirm that Kashf is not an ability granted to everyone. God is in fact the one who does the unveiling once a person has given up on all worldly forms of knowledge and his/her heart is pure and open for God. It is God's will to choose what people see and which people see. Ibn ‘Arabi calls this “inner receptivity” to the manifestation ("tajalli") of the Divine Mysteries, the essence of which is "mukashafa".
Peripatetic Scholars vs. Sufis.
Peripatetic scholars such as Avicenna, al-Kindi, and al-Farabi argue that the intellect unaided by divine unveiling ("kashf") is sufficient in order for man to attain ultimate truth.
Sufis such as Bayazid Bastami, Rumi, and Ibn al-Arabi, contrarily argue that the limited human intellect is insufficient and misleading as a means of understanding ultimate truth. This kind of understanding requires intimate, personal, direct knowledge resulting from the removal of the veils separating man from God as given to man by God himself. This is "kashf".
Other Types of "Kashf".
The 18th century mystic Khwaja Mir Dard (d. 1785) (, relying upon the traditional terminology, classified the revelations as follows in his `Ilm al-Kitab: