Ḥuzn (sorrow) is the prevention of the nafs (the lower self) from being distracted by joy... Rābiʿa al-ʿAdawiyya once heard a man say, "Take this sorrow away from me!" She replied to him: "How little sorrow I have! If you were truly sorrowful, you would not even be able to breathe."
Sufyān ibn ʿUyayna also said: "If a sorrowful person among the umma (community) weeps, Allah, the Exalted, shows mercy to that umma because of that weeping."
The prevailing ḥāl (spiritual state) of Dāwūd al-Ṭāʾī was ḥuzn. At night, he would supplicate: "My God! Your affliction has swept away all other afflictions from me, it has come between me and my sleep."
It has been said: "A person upon whom new misfortunes constantly descend—how can he find consolation or escape from sorrow? Ḥuzn prevents eating and drinking, and khawf (fear of God) prevents sinning."
When one of the Sufis was asked, "How can it be known that a person is sorrowful?" he replied: "By the abundance of his groaning."
Sirrī al-Saqaṭī said: "I wish that all the sorrow of mankind were mine."
The Sufis have advanced various opinions about ḥuzn, but they have agreed on this point: Sorrow related to the Hereafter is praiseworthy, but sorrow related to the dunyā (the world) is not something praiseworthy.
Nevertheless, Abū ʿUthmān al-Ḥīrī holds the view that every kind of ḥuzn is a virtue and an increase (a valuable quality) for the muʾmin (believer). However, the cause of sorrow should not be a maʿṣiyya (sin, disobedience); a believer should not be sorrowful for being unable to commit a sin for this or that reason. For even if sorrow does not elevate the servant's rank, it erases his sins. (Qushayrī, 71)
The ḥaqīqa (inner reality) of ḥuzn is to lose the beloved and to be prevented from one's desire. The ḥaqīqa of wajd (ecstasy) is to attain one's desire. The difference between ḥuzn and wajd is this: ḥuzn is the name for the sorrow that befalls the nafs; wajd is the name for the sorrow that arises, depending on the beloved, concerning another's share. All these changes are due to fate.