Ruling on cursing specific people
Question

What is the ruling on cursing (and not just insulting) the Jews and Christians or other groups, whether living or dead? May Allah reward you with good.
Praise be to Allah.The author of Lisaan al-‘Arab [a famous Arabic-language dictionary – Translator] said: La’n (curse) means being cast out far from goodness, and it was said that it means being cast away far from Allah, and from people. 
Cursing happens in two ways: 
Cursing the kuffaar and sin in general terms, such as saying “May Allah curse the Jews and Christians,” or “May Allah curse the kaafirs, evildoers and wrongdoers,” or “May Allah curse the wine-drinker and thief.” This kind of curse is permissible and there is nothing wrong with it. Ibn Muflih said in al-Adaab al-Shar’iyyah, 1/203: “It is permissible to curse the kuffaar in general.” 
The second is where the curse is applied to a specific person, whether he is a kaafir or an evildoer, such as saying, “May Allah curse So and so,” mentioning him by name. This may fall into one of two categories: 
1 – Where there is a text which states that he is cursed, such as Iblees, or where there is a text which states that he died as a kaafir, such as Pharaoh, Abu Lahab and Abu Jahl. Cursing such persons is permitted. 
Ibn Muflih said in al-Adaab al-Shar’iyyah, 1/214: “It is permissible to curse those concerning whom there is a text stating that they are cursed, but there is no sin involved if one does not do this.” 
2 – Cursing a particular kaafir or evildoer concerning whom there is no text stating that they are cursed – such as wine-drinkers, those who offer sacrifices to anything other than Allah, the one who curses his parents, those who introduce innovations in religion, and so on. 
“The scholars differed as to whether it is permissible to curse these people, and there are three points of view:
(i)That it is not permissible under any circumstances
(ii)That it is permissible in the case of a kaafir but not of a (Muslim) evildoer
(iii)That it is permissible in all cases.”
Al-Adaab al_Shar’iyyah by Ibn Muflih, 1/303 
Those who say that it is not permissible quoted a number of texts as evidence, including the following: 
1 – The report narrated by al-Bukhari (4070) from ‘Abd-Allah ibn ‘Umar, that he heard the Messenger of Allah (peace and blessings of Allah be upon him), when he raised his head from rukoo’ in the final rak’ah of Fajr prayer and said: “O Allah, curse So and so, and So and so, and So and so,” after he had said, “Sami’a Allahu li man hamidah, Rabbana wa laka’l-hamd.” Then Allah revealed the words (interpretation of the meaning): 
“Not for you (O Muhammad, but for Allah) is the decision; whether He turns in mercy to (pardons) them or punishes them; verily, they are the Zaalimoon (polytheists, disobedients and wrongdoers)” [Aal ‘Imraan 3:128]
2 – The report narrated by al-Bukhari (6780) from ‘Umar, that there was a man at the time of the Messenger of Allah (peace and blessings of Allah be upon him) whose name was ‘Abd-Allah, but his nickname was Himaar (donkey), and he used to make the Messenger of Allah (peace and blessings of Allah be upon him) laugh. The Prophet (peace and blessings of Allah be upon him) had him (previously) flogged for drinking, then he was brought one day and he commanded that he be flogged, and a man who was there said, “O Allah, curse him, how often he is brought [for this reason]!” But the Prophet (peace and blessings of Allah be upon him) said: “Do not curse him, for by Allah what I know about him is that he loves Allah and His Messenger.” 
Shaykh al-Islam Ibn Taymiyah said in Majmoo’ al-Fatawa, 6/511. 
It is permissible to curse all those whom Allah and His Messenger have cursed, but as for cursing specific people, if it is known that the person died in kufr, then it is permissible to curse him. But with regard to a specific [Muslim] evildoer, we should not curse him, because the Prophet (peace and blessings of Allah be upon him) forbade cursing ‘Abd-Allah ibn Himaar who used to drink wine, even though he had cursed the wine-drinkers in general; however cursing a specific person if he is an evildoer or promoter of bid’ah is a point of dispute among the scholars. 
And Shaykh Ibn ‘Uthaymeen said in al-Qawl al-Mufeed, 1/226. 
The difference between cursing a specific person and cursing those who commit sin in general is that the former (cursing a specific person) is not allowed, and the latter (cursing the people who commit sin in general) is allowed. So if you see an innovator, you do not say, ‘May Allah curse you,’ rather say, ‘May the curse of Allah be upon those who introduce innovations,’ in general terms. The evidence for that is the fact that when the Prophet (peace and blessings of Allah be upon him) cursed some people among the mushrikeen and followers of jaahiliyyah and said: “O Allah, curse So and so, and So and so, and So and so,” he was told not to do that when Allah said (interpretation of the meaning): 
“Not for you (O Muhammad, but for Allah) is the decision; whether He turns in mercy to (pardons) them or punishes them; verily, they are the Zaalimoon (polytheists, disobedients and wrongdoers)”[Aal ‘Imraan 3:128]
This was narrated by al-Bukhari. 
And Allah knows best.