O son, fana (annihilation) is one rather difficult terminology which frequently pops up in the studies of Sufism. It has to because it is one major pre-requisite in reaching God. Below is the essence of fana as expounded by a venerable Sufi saint of the 11th century - Khwaja Abdullah Ansari of Herat. May with his blessings, Allah unveils to us the reality of our true selves.
The 99th Ground is Annihilation. The Ground of Annihilation arises from the (98th) Ground of Direct Observation (mu'ayana). God Almighty states: "All things perish except His Face. His is the Judgment and unto Him you shall be returned." (Qur'an XXVII: 88)
Annihilation is naughting, and this naughting occurs through three things in three things:
i. Annihilation of seeking in the Found
ii. Annihilation of knowledge in the Known
iii. Annihilation of sight in the Seen
How can 'that which is naught' ever find out anything about 'that-which-eternally-is'? How can Reality - Eternally Subsistent - ever be aligned with a merely nominal perishable phenomenon? What can bind the Worthy to the unworthy?
All save Him are juxtaposed between three things:
today which has gone astray and been mislaid and
Thus, all save He, are non-existent and yet existent by Him. So all existence is His. The raindrop reached the sea and found therein its mellowing, just as the star by daylight was effaced. Whoever reaches his Lord, has attained his 'self'.______________________________________
Reference: Essay by A.G. Ravan Farhadi in 'The Heritage of Sufism'. Published by Oneworld Oxford.
Related Lisan al-Din post: The Ground of Direct Observation