In the name of God, the Merciful, the Compassionate.
Someone asked the eminent shaykh Abu ‘Ali b. Sina (may God the Exalted have mercy on him) the meaning of the Sufi saying, He who knows the secret of destiny is an atheist. In reply he stated that this matter contains the utmost obscurity, and is one of those matters which may be set down only in enigmatic form and taught only in a hidden manner, on account of the corrupting effects its open declaration would have on the general public. The basic principle concerning it is found in a Tradition of the Prophet (God bless and safeguard him): Destiny is the secret of God; do not declare the secret of God. In another Tradition, when a man questioned the Prince of the Believers, ‘Ali (may God be pleased with him), he replied, Destiny is a deep sea; do not sail out on it. Being asked again he replied, It is a stony path; do not walk on it. Being asked once more he said, It is a hard ascent; do not undertake it.
The shaykh said: Know that the secret of destiny is based upon certain premisses, such as 1) the world order, 2) the report that there is Reward and Punishment, and 3) the affirmation of the resurrection of souls.
— Avicenna, On the Secret of Destiny (tr. George Hourani)