Two hadîth-i-sherîfs read as follows: “Do not pronounce maledictions over yourselves or over your offspring. Acquiesce in what Allâhu ta’âlâ foreordained. Pray so that He will increase His blessings.” “Maledictions pronounced over you by your parents or by the oppressed over their oppressor will not be rejected (by Allâhu ta’âlâ).” A person who prays that another Muslim should become a disbeliever becomes a disbeliever himself. Desiring that an oppressing person should die as a disbeliever so that he may suffer eternal punishment, would not cause disbelief. The Qur’ân al-kerîm informs us that Mûsâ (Moses) ‘alaihis-salâm’ made a similar malediction. Imâm a’zâm Abû Hanîfa ‘rahimahullâhu ta’âlâ’ stated that it would cause a state of disbelief to wish that someone else should become a disbeliever. It is forbidden (harâm) to pronounce a malediction over anyone, with the exception of one’s oppressor. It is permissible to pronounce a malediction over one’s oppressor with an earnestness and vehemence equivalent to the degree of the injustice perpetrated.
Anything permissible should (only) countervail the ’udhr (, i.e. the reason,) which makes it (canonically) permissible (, i.e. jâiz). If you are patient enough not to pronounce a malediction over someone who has wronged you, then so much the better; and forgiving is the best. It is not permissible to say “May Allâhu ta’âlâ give you a long life” to any disbeliever or to a non-Muslim citizen of an Islamic state. It is permissible to make such a prayer with the following intentions, e.g., in order for him to become a Muslim or in order for him to pay his taxes so that Muslims will become more powerful. A person who greets a disbeliever, (by saying ‘salâmun ’alaikum’ and) with reverence, becomes a disbeliever. Saying any word which would come to mean a reverence to a disbeliever causes disbelief. For example, saying “My master” to a disbeliever causes disbelief.
Ref: This paragraphes are quoted from the book “Ethics of Islam” page 151, which is the translation of the book Berîka written by Abû Sa’îd Muhammad bin MustafâHâdimî ‘rahima hullâhu ta’âlâ’, who passed away in 1176 Hijrî, 1762 A.D. in Konya / Turkey and the book Akhlâq-i-Alâî written in Turkish by Alî bin Amrullah ‘rahimahullâhu ta’âlâ,’ who passed away in 979 Hijrî, 1572 A.D. in Edirne / Turkey. You can find the whole book and the other valuable books in the web site www.hakikatkitabevi.com.tr and download in PDF format for Adobe Acrobat Reader, EPUB format for iPhone-iPad-Mac devices and MOBI format for Amazon Kindle device.