Praise be to Allah, the Lord of the Worlds; and may His blessings and
peace be upon our Prophet Muhammad and upon all his Family and
Companions.
It is lawful for you to ask Allah to punish this
Muslim as Allah Says (interpretation of meaning):
{"Allah does not like that the evil should be
uttered in public except by him who has been wronged….}[4:148].
Ibn Abbas said: Allah does not like that the person ask imprecation for
someone except if they offend them. However, not asking punishment for
him and pardoning such a person is better as Allah Says (interpretation
of meaning):
{…but whoever forgives and makes
reconciliation, his reward is with Allah….}[42:40].
Allah also Says (interpretation of meaning):
{… Let
them pardon and forgive. Do you not love that Allah should forgive
you?…}[24:22].
The Prophet (peace be upon him) also said:
Indeed Allah has not increased the one who pardons except by more
prestige...
[Reported by Imam Muslim].
As for insulting him it should not go beyond what
he did to you and forgiving him is better.
However, cursing him is unlawful. Abu Dawood
reported that the Prophet (peace be upon him) said:
When the person curses something, the curse ascends to Heavens. But the
gates of Heavens get closed before it. Then the curse falls down on
earth, but its gates get closed as well in front of it. Upon that the
curse moves left and right and if it does not find anywhere to stay it
returns to the thing cursed if it deserves it, it stays there.
Otherwise, it returns to the one who uttered it. So, this is a great
threat for those who curse what does not deserve to be cursed.
Abu Dawood and al-Tirmizi reported that the Prophet (peace be upon him)
said:
Do not curse one another with the curse of Allah.
The author of 'Tuhfat Al-awazi' said: None of you should curse the other
saying: 'May the Curse of Allah befall you'. Al-Bukhari and Muslim also
reported that the Prophet (peace be upon him) said:
Cursing the Muslim is like killing him. So, the Muslim should beware of
cursing fellow Muslims.
Allah knows best.
