The Prohibition of Engaging in Destructive Acts in Islamic and Non-Islamic Countries - حرمة القيام بالأعمال التخريبية في البلاد الإسلامية وغير الإسلامية
Note: This was originally a Fatwa, from cp.Alukah.net, but it was only in Arabic, so this is its translation :
Question:
Is carrying out assassinations and bombings in government facilities in non-Muslim countries considered a necessity and an act of jihad? May Allah reward you with goodness.
Answer:
No, this is not permissible. Assassinations and acts of sabotage are not allowed because they bring harm to Muslims, leading to their killing and displacement.
Such actions are impermissible. What is prescribed regarding non-believers is jihad in the path of Allah, and confronting them in battles if Muslims have the capability. They should prepare armies and fight the non-believers as the Prophet (peace be upon him) did. However, sabotage and assassinations only bring harm to Muslims.
When the Prophet (peace be upon him) was in Mecca before the migration, he was commanded to restrain from fighting: *"Have you not seen those who were told to restrain their hands (from fighting) and establish prayer and give zakah?"* (Quran 4:77).
He was commanded to refrain from fighting the non-believers because they did not have the capability to do so. Had they killed any of the non-believers, the non-believers would have exterminated them completely, as they were stronger and had power over them.
Assassinations lead to the killing of Muslims residing in those countries, as you witness and hear about today. This is not part of the call to Islam, nor is it jihad in the path of Allah. It brings harm to Muslims. Similarly, sabotage and bombings also bring harm to Muslims, as is evident. When the Prophet (peace be upon him) migrated and had an army and supporters, he was then commanded to engage in jihad against the non-believers.
Did the Prophet (peace be upon him) and his companions kill non-believers while they were in Mecca? Absolutely not; they were prohibited from doing so.
Did they destroy the property of non-believers while in Mecca? Absolutely not; they were prohibited from doing so. They were only commanded to preach and convey the message. Enforcement and fighting were only prescribed in Medina, when Islam had established a state.
Mufti: Sheikh Saleh Al-Fawzan - "Illuminating Words from the Esteemed Scholars" (pp. 113-114)