Shihabudin Yahya Suhrawardi (1155 - 1191 CE), a remarkable Sufi and philosopher from Iran is well known for his Illuminationist Philosophy arising from his book called Kitab Hikmat al-Ishraq (The Philosophy of Illumination).
He also authored Lughati Muran (The Language of the Termites) which explains the knowledge needed by the seeker in knowing God, himself and all creations. The quotation below is from the said book; advice from Suhrawardi for those wishing to attain inner illmunination (ishraq).
"Whatever hinders good is evil and whatever blocks the (spiritual) Path is infidelity (kufr) for men.
To be contented with whatever one's sensual self (nafs) presents and to adapt oneself to it, is impotence on the path of mystical progression (dar tariq-i suluk).
To look with delight upon oneself - even if one have God in mind - is ruination.
Salvation is to turn one's face utterly towards God."
Reference: Essay by Mehdi Aminrazavi in "The Heritage of Sufism"
Further reading on Suhrawardi: tebyan.net