حَدَّثَنَا إِسْمَاعِيلُ، حَدَّثَنَا أَيُّوبُ، عَنِ الْحَسَنِ
قَالَ: قَالَ رَجُلٌ لِلزُّبَيْرِ أَلَا أَقْتُلُ لَكَ عَلِيًّا قَالَ: كَيْفَ تَقْتُلُهُ قَالَ أَفْتِكُ بِهِ قَالَ: لَا قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ الْإِيمَانُ قَيْدُ الْفَتْكِ لَا يَفْتِكُ مُؤْمِنٌ
A man said to Az-Zubayr: “Shall I kill Ali for you?” He said: “How would you kill him?” He said: “I will assassinate him.”He said: “No, the Messenger of Allah (sallallahu alayhi wa sallam) said: Faith prohibits assassination; no believer should resort to that.”.
Musnad Ahmad 1354, Book 7, The Musnad of az-Zubair bin al-'Awwam, Hadith 26. 1 min read