The Method of the Righteous (Minhaj al-Salihin): The veil (al-hijab) is the imprinting of cosmic forms upon the heart, which prevents the acceptance of the divine manifestation (tajalli) of the Truth.

Whenever there is anything other than Allah the Exalted within the heart of the wayfarer, he is veiled from the manifestation of the Truth. These extraneous things (al-aghyar) may multiply, becoming a dark veil, or they may diminish, becoming a luminous veil. For this reason, the verified masters chose for the wayfarer the abandonment of secondary causes (tark al-asbab), and the adoption of seclusion (al-khwalwah) and isolation from people, so that cosmic forms are not imprinted upon his heart and do not bar him from the manifestation of the Truth to him.

When the wayfaring unto Allah reaches its ultimate end, the servant becomes fully immersed in the ocean of divine unity (al-tawhid) and gnosis, where his essence dissolves into His Essence, and his attributes into His Attributes. He vanishes from everything other than Allah, seeing nothing in existence except Allah the Exalted. This is what they term "annihilation in divine unity" (al-fana' fi al-tawhid).