Islam forbids Muslims from imprecating (invoking curse on) themselves and other Muslims. Our Prophet (p.b.u.h.) enjoins:
“Do not curse your own selves, your children, or your belongings lest your curse coincides with the time when Allah is about to confer upon you what you demand and thus your prayer may be readily answered.” (Riyad-us Saleheen Translation, III, 82)
Our Prophet (p.b.u.h.) used to avoid invoking curse. He used to tell that He was the prophet of mercy, rather than being a prophet that communicates curses.
When He went to Taif to convey Islam at Meccan era, He had encountered wrong behaviors; He was stoned and His feet were drenched in blood. In the meantime, Allah had communicated Him that “the curses He would invoke on them would be accepted and they would be destroyed if He prayed.” But our Prophet (p.b.u.h.) had responded “No my Lord, there might come about children from them, who will worship You!”
He had prayed for His enemies at Uhud, who had broken his tooth and wounded his face: “O my Lord! Lead my people to the right path, because they do not know what they do.” (Tajrid-i Sareeh Translation, IV, 314)
When He was requested to imprecate upon the People of Devs, who did not convert to Islam despite rather hard work, He had said: “O my Lord, Lead the People of Devs to the right path and adjoin them to us.” (Tajrid-i Sareeh Translation, VIII, 344)
Besides, there has been times when our Prophet had invoked curses upon enemies of Allah. The Messenger of Allah had invoked curses on the People of Kilab for a month, who had martyred seventy inviters of Islam at Bi’r-i Mauna.
He had invoked curses on the polytheists that had made sports of him while he was performing his prayer at the Kaaba and saw them dead during Bedir War with his own eyes. (Tajrid-i Sareeh Translation, X; 43-45)
He had prayed for the destruction of the enemy gathered around Madina at Handak War and a storm sourcing from east had turned them upside-down that night. (Tajrid-i Sareeh Translation, VIII, 342-343)
After all, we can say that a Muslim should avoid invoking curses on other Muslim, even though they happen to be sinners, but should suppose calling down curses on explicit enemies of Islam as a religious duty in case.
SOURCE: Durak Pusmaz, “Beddua”, Şamil İslam Ansiklopedisi.