عَنِ الْحَسَنِ رَضِيَ اللَّهُ عَنْهُ قَالَ جَاءَ رَجُلٌ إِلَى الزُّبَيْرِ بْنِ الْعَوَّامِ رَضِيَ اللَّهُ عَنْهُ فَقَالَ أَقْتُلُ لَكَ عَلِيًّا قَالَ وَكَيْفَ تَقْتُلُهُ وَمَعَهُ الْجُنُودُ قَالَ أَلْحَقُ بِهِ فَأَفْتِكُ بِهِ قَالَ لَا أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ إِنَّ الْإِيمَانَ قَيْدُ الْفَتْكِ لَا يَفْتِكُ مُؤْمِنٌ
It is narrated from Hasan that a man came to Sayyiduna Zubair bin Al-Awwam (may Allah be pleased with him) and said: Shall I kill Ali (may Allah be pleased with him) for you? He replied: How will you kill him when he has armies with him? The man said: I will apparently join him, and then, finding him unaware, I will kill him. He said: No, do not do that, because the Messenger of Allah (peace and blessings be upon him) said: Faith prevents killing after granting protection; a believer does not kill after granting protection.