Al-Matalib al-'Aliyah 4440 — The virtue of one who kills

It is narrated from Qays bin Abbad that Sayyiduna Ali (may Allah be pleased with him) held back from fighting the people of Nahrawan (the Khawarij) until they themselves committed some act of fitnah and mischief. Then those people set out and came to Sayyiduna Abdullah bin Khabbab (may Allah be pleased with him), who was staying in a village of his and had completely withdrawn from the fitnahs. The Khawarij seized him. The narrator said: Meanwhile they saw a date fall from a date palm; one of them picked it up and put it in his mouth. His companions rebuked him and said: "This is a date belonging to the people of the covenant (the non-Muslim subjects of the Islamic state); how could you take it without paying its price?" So he immediately spat it out of his mouth (lafazaha, meaning "he spat it out"). Then they passed by a pig, and one of them struck it with his sword and killed it. Again his companions objected: "You have (wrongfully) killed one of the pigs of the people of the covenant?" Then Sayyiduna Abdullah bin Khabbab (may Allah be pleased with him) said to them: "Shall I not tell you about one whose right and sanctity over you is far greater than this date and this pig?" They asked: "Who is that?" He said: "It is I." (The narrator thinks he also said:) "Since I reached maturity I have never left a single prayer, nor missed a fast of Ramadan," and he listed several other good deeds of his. But those wrongdoers seized him, slaughtered him and martyred him. When this news reached Sayyiduna Ali (may Allah be pleased with him), he ordered his companions to advance against them, and he demanded of the Khawarij: "Give us retaliation (qisas) for the blood of Abdullah bin Khabbab." They replied: "How can we give you retaliation for him when all of us together killed him?" On hearing this, Sayyiduna Ali (may Allah be pleased with him) called out loudly, "Allahu Akbar" (Allah is the Greatest), and said to his companions: "Attack them! By Allah, not even ten of you will be killed, and not even ten of them will escape." And so it happened (that is, the Khawarij were completely wiped out). After that Sayyiduna Ali (may Allah be pleased with him) said: "Search for a man whose bodily signs are such and such." The people searched for him but did not find him; then they searched again and found him. Sayyiduna Ali (may Allah be pleased with him) asked: "Who recognises him?" No one recognised him. One man said: "I saw this man at al-Najaf, and he was saying: I want to go to this city, where I have no kin and no one who knows me." Sayyiduna Ali (may Allah be pleased with him) said: "You have spoken the truth; he was one of the jinn."
Musaddad recorded this narration in his Musnad (al-Matalib al-'Aliyah: 4440). Its chain includes eminent, trustworthy (thiqah) imams such as Yahya bin Sa'id al-Qattan and Sulayman al-Taymi, which strengthens the historical and scholarly standing of this incident.