The meaning of tahaqquq is tahqīq (realization is verification). Just as taʿallum (learning) is taʿlīm (instruction), ḥaqīqa (inner reality) is a noun and ḥaqāʾiq is its plural. The meaning here is that the qalb (the heart), in the presence of the existent in which it believes, always remains by receiving its share. If a doubt or ḥayāl (illusion) intervenes in the qalb regarding what it believes, preventing it from remaining in the presence of the One, then the iman (faith) becomes bāṭil (invalid). (Lumaʿ, 413)
Tahqīq is a maqām (spiritual station) in which no doubt that would impair it is accepted. The possessor of this attribute is called a muḥaqqiq. Tahqīq is to know everything that you seek from the Real (al-Ḥaqq) regarding His essence. (The Real) fulfills this request in terms of knowledge. If there is agreement in acting upon this, He grants it as a ḥāl (spiritual state). In this case, the person becomes one in whom the power of tahqīq has manifested. If it does not manifest upon him, he knows that he has made a mistake, but this error does not cause any damage to his essential reality. For he has erred due to being under an influence. There is a divine secret here: that Allah is the absolute Ḥakīm (Wise) and the One who puts everything in its proper place. He is the Giver of all things to His creation. According to Allah's arrangement, there is no error in the cosmos. The Lord knows, through this tahqīq, the state of the muḥaqqiq who realizes it. He also knows that he has erred. But this error, since Allah has placed him there in that way, is not named an error in relation to the servant's state with respect to Allah, but only in relation to the servant's own state. Even in the error of the one possessing tahqīq, there is reward. This means: just as the mujtahid who does not err in the foundation of the matter receives two rewards in the sight of Allah, so does he. His ruling is established. His error is only an error in that his evidence does not correspond to someone else's evidence, to the sharia (the sacred law), or to the ḥaqq (truth). Such is the rank of tahqīq and the muḥaqqiq. Among the necessary conditions for the possessor of this station is that his hearing, sight, hand, foot, and all his faculties he employs are of the Real (al-Ḥaqq). Thus, he acts only with the Real, in the Real, and for the Real. This quality is valid only for the maḥbūb (beloved servant). The servant does not become maḥbūb until he draws near (to Allah). And nearness is not possible without supererogatory good deeds (nāfila). But even nāfila good deeds are not valid for him unless the obligatory (farḍ) acts are perfected. And the obligatory acts do not reach perfection unless their rights are fulfilled. (Futūḥāt, II, 264–265)
Tahaqquq is to witness the Real (al-Ḥaqq) in the world, which is the form of His names. The Real, who is the muḥaqqiq, is never veiled from creation by creation, nor from the Real by preoccupation with the Real. (Kāshānī, 156)
The people of tahqīq (ahl al-tahqīq) are divided into three: the first are those who unite transmitted knowledge (khabar) with rational reflection (naẓar); the second are those who unite comparison (tashbīh) with transcendence (tanzīh); the third are those who unite incapacity (ʿajz) with sacred union (ittiḥād). (Rawḍa, 439)
Tahqīq is to take the essence of what comes from the Real (al-Ḥaqq). Its first subtlety is that your knowledge does not compete with His knowledge; its second subtlety is that your witnessing does not conflict with His witnessing; its third subtlety is that your sign does not efface His sign. (Rawḍa, 496)
Tahqīq is to witness the Real (al-Ḥaqq) in the world, which is the form of His names. The muḥaqqiq is not veiled from creation by the Real, nor from the Real by creation. (Jāmiʿ, 79)
To establish a matter with its own evidence is tahqīq; to establish it with another evidence is tadqīq; to express it with effective phrases is tarkīq; to observe the sciences of rhetoric (badīʿ and maʿānī) in its composition is tanmīq; and to leave no room for objection in that matter is tawfīq. (Qawānīn, 61)