In the name of Allah, and may Allah's Peace and blessings be upon the Messenger of Allah.
Islam prohibits harming civilians, either by insult, hitting, killing or any kind of harming or terrorizing. It is recorded in Sahih Muslim that Prophet Muhammad (PBUH) said, "He who points a weapon towards his brother the angels invoke curse upon him even if he is his real brother so long as he does not abandon it (the pointing of weapon towards one's brother Muslim)".
Imam Al-Nawawi, may Allah have mercy on him, "This hadith underscores the inviolability of Muslims and the absolute prohibition of terrorizing, frightening or harming him. Prophet Muhammad's (PBUH) saying: 'if he is his real brother' is an emphasis on the comprehensiveness of prohibition to include all people and all cases; whether they are expected to commit crimes against them or not, and whether it is done intentionally or kiddingly. This is because one may lose control of the arm at any moment."
It is recorded in Sunan Abu Dawud that Prophet Muhammad (PBUH) said, "It is not lawful for a Muslim to frighten another Muslim".
This applies simply to the prohibition of pointing a weapon towards Muslims and terrorizing them, so what about the one who kills his fellow Muslim or even frightens him. The one who does these acts is in fact fights Allah and his Messenger and spreads corruption on earth and thus deserves the punishment of the oppressors in this world and grave torment in the hereafter. Allah, the Almighty, says, "Indeed, the penalty for those who wage war against Allah and His Messenger and strive upon earth [to cause] corruption is none but that they be killed or crucified or that their hands and feet be cut off from opposite sides or that they be banished from the land. That is for them a disgrace in this world; and for them in the Hereafter is a great punishment." (The Qur'an, 5:33) In his Farewell sermon, Prophet Muhammad (PBUH) highlighted the sacredness of people's lives and blood in order to preserve people's stability and security, as recorded in Sahih Al-Bukhari: "Verily your blood, your property and your honour are as sacred and inviolable as the sanctity of this day of yours, in this month of yours and in this town of yours. Verily! I have conveyed this message to you."
Whoever carries weapons against us with the aim of frightening, killing or terrorizing us is, in fact, not following our way or religion. It is narrated on the authority of Abdullah Ibn 'Umar, may Allah be pleased with them both, that Prophet Muhammad (PBUH) said, "Whoever carries arms against us, is not one of us."
Therefore, we should abstain from all forms of violence, extremism and terrorism and denounce and crack down on all those who carry out such acts which are absolutely prohibited by Islamic Shariah in order to get rid of all corruptors and aggressors in our society.
And it is Allah Whom we seek help!