"الإِيمان قيدُ الْفَتْكِ، لَا يفتَكُ مُؤمنٌ" .
The Prophet ﷺ said: Faith prevented assassination. A believer should not assassinate.
عَنِ النَّبِيِّ ﷺ قَالَ الإِيمَانُ قَيَّدَ الْفَتْكَ لاَ يَفْتِكُ مُؤْمِنٌ
A man came to az-Zubair bin al-’Awwam ؓ and said: “Shall I kill ʿAli for you?” He said: “No; how can you kill him when he has the troops with him?” He said: “I will catch up with him and assassinate him.” He said: “No. The Messenger of Allah ﷺ said: Faith prohibits assassination; no believer should resort to that.” Al-Hasan said: A man came to az-Zubair bin al-ʿAwwam ؓ and said: “Shall I not kill ʿAli for you?” He said: “How can you kill him when he has people with him?” (and he narrated a similar report.)
لَا إِنَّ رَسُولَ اللهِ ﷺ قَالَ إِنَّ الْإِيمَانَ قَيَّدَ الْفَتْكَ لَا يَفْتِكُ مُؤْمِنٌ
A man came to az-Zubair bin al-’Awwam ؓ and said: “Shall I kill ʿAli for you?” He said: “No; how can you kill him when he has the troops with him?” He said: “I will catch up with him and assassinate him.” He said: “No. The Messenger of Allah ﷺ said: Faith prohibits assassination; no believer should resort to that.” Al-Hasan said: A man came to az-Zubair bin al-ʿAwwam ؓ and said: “Shall I not kill ʿAli for you?” He said: “How can you kill him when he has people with him?” (and he narrated a similar report.) (Using translation from Aḥmad 1426)
قَالَ رَسُولُ اللَّهِ ﷺ «لَا يَفْتِكُ الْمُؤْمِنُ الْإِيمَانُ قَيْدُ الْفَتْكِ»
"لَيسَ فِي الإِسْلامِ إِيمَاءٌ وَلَا فَتْكٌ، إِنَّ الإِيمَانَ قَيدُ الفَتْكِ، وَالنَّبِيُّ لَا يُومِئُ".