Maktub (lit. “written”, “ordained”). In the sense of “it is written”, it is an expression pronounced frequently in resignation to God’s Providence. It refers to the Divine decrees written on al-lawh al-mahfuz (the “guarded tablet”), and to such Koranic statements as: “There befalls not any happening in the earth or in your souls except it is in a book [Kitab] before We [God] manifest it…” (57:22). Ibn ‘Ata’ Allah says in the Hikam:
Antecedent intentions [sawabiq al-himam] cannot pierce the walls of predestined Decrees [aswar al-aqdir].
While Islam views man’s life as predestined in the sense that nothing can finally oppose the Will of God, man nonetheless has the gift of free will in that he does make choices and decisions. Resignation to the Will of God is a concomitant to striving in the Path of God. Above all, man is completely free in what is essential, that is, he can accept the Absolute and surrender himself to It, or reject God and pay the price. In this he has absolute free-will. The Talmud also says: “Everything is in the Hands of God, except the Fear of God.”
Source: Cyril Glassé, The Concise Encyclopedia of Islam, Third Edition, p. 319