When knowledge and ru'yet (vision, direct seeing) are combined, the unseen (ghayb) is unveiled to the one who possesses them. The servant attains certainty (yaqīn) through knowledge, direct witnessing (mushāhada), and the reality of seeing with iman (faith). (Bayān, 62)
The center of ru'yet is the fuʾād (the spiritual heart). Allah the Exalted has said, "The heart did not lie [about] what it saw" (al-Najm 53:11). The word fuʾād is derived from the word fāʾida (benefit), because it will see the benefits of its love from Allah the Exalted; the heart benefits through seeing, and the qalb (the heart) tastes through knowledge. If the heart does not see, the qalb cannot benefit. (Bayān, 68)
Ru'yet is not seeing with basīra (inner sight), but rather witnessing with the eye. (Istilāh, 540)
Even if the possible existents (mumkināt) are infinite, they are non-existent (maʿdūm). They are entities that can be seen under the witnessing of the Real (al-Ḥaqq). We cannot attribute seeing to a cause through existence (wujūd); rather, we can only attribute things to a cause (we can ascribe existence to things, but not to seeing). Whether something is in itself non-existent or existent, if it is something that can be seen, it is receptive to the relation of the act of seeing. Even if the possible existents are infinite, they are seen by Allah the Exalted. This (seeing) is not by the relation of knowledge, but rather it is of another kind called ru'yetu kānat mā kānat (seeing as it is). (Esfār, 25)
Mushāhada (direct witnessing) is the seeing of the shāhid (witness, sign) that comes from the Real (al-Ḥaqq) in the heart. Mushāhada that is bound by the condition of a sign or ru'yet (seeing) is not of this kind. For this reason, Moses (peace be upon him) said, "My Lord, show Yourself to me that I may look at You" (al-Aʿrāf 7:143); he did not say, "Let me directly witness You." Because He (God) cannot be seen, but can only be witnessed. What was hidden from Moses was shown to him. (Esfār, 66)