Musannaf Ibn Abi Shayba 36:479

Abu Khalid al-Ahmar narrated to us, from Ibn Ishaq, from Yazid ibn Abdullah ibn Qusayt, from al-Qa'qa' ibn Abdullah ibn Abi Hadrad al-Aslami, from his father, Abdullah ibn Abi Hadrad, who said: The Messenger of Allah (peace and blessings of Allah be upon him) sent us in a military expedition to Idam. He said: We met Amir ibn al-Adbat. He said: He greeted us with the greeting of Islam, but we refrained from him. Then Muhallim ibn Jaththama attacked him and killed him. When he killed him, he took his camel and some goods he had. When we arrived, we brought his matter to the Messenger of Allah (peace and blessings of Allah be upon him) and informed him of his affair. Then this verse was revealed: "O you who have believed, when you go forth in the cause of Allah, investigate; and do not say..." [to the end of the verse]. Ibn Ishaq said: Muhammad ibn Ja'far informed me, from Zayd ibn Damira, who said: My father and my uncle narrated to me—and they had both witnessed Hunayn with the Messenger of Allah (peace and blessings of Allah be upon him)—they said: The Messenger of Allah (peace and blessings of Allah be upon him) prayed Dhuhr, then sat under a tree. Al-Aqra' ibn Habis, who was the leader of Khandaf, stood up to him, defending Muhallim, and Uyayna ibn Hisn stood up seeking the blood of Amir ibn al-Adbat al-Qaysi, and he was from Ashja'. He said: I heard Uyayna ibn Hisn saying, "I will surely make his women taste of grief like what he made my women taste." The Prophet (peace and blessings of Allah be upon him) said: "Will you accept the blood money?" They refused. Then a man from Banu Layth called Muktayl stood up and said: "By Allah, O Messenger of Allah, I have not likened this slain man in the glory of Islam except to sheep that came to water, then were shot at, so the last of them fled. Establish [the law] today and change it tomorrow." He said: The Prophet (peace and blessings of Allah be upon him) said with his hands: "You shall have fifty [camels] in this journey of ours, and fifty when we return." He said: So they accepted the blood money. He said: They said, "Bring your companion so that the Messenger of Allah (peace and blessings of Allah be upon him) may seek forgiveness for him." He said: So he was brought, and his adornment had reached him, and he was wearing a garment in which he had prepared himself for death, until he was made to sit before the Prophet (peace and blessings of Allah be upon him). He said: "What is your name?" He said: "Muhallim ibn Jaththama." The Prophet (peace and blessings of Allah be upon him) said with his hands—and he described that he raised them—: "O Allah, do not forgive Muhallim ibn Jaththama." He said: We talked among ourselves that he only manifested this, while he had sought forgiveness for him in secret. Ibn Ishaq said: Amr ibn Ubayd informed me, from al-Hasan, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to him: "Did you grant him security by Allah, then kill him?" By Allah, he did not remain but seven [days] until Muhallim died. He said: I heard al-Hasan swearing by Allah that he was buried three times, and each time the earth cast him out. He said: So they placed him between two mountain slopes and piled stones upon him, but the beasts of prey ate him. They mentioned his matter to the Messenger of Allah (peace and blessings of Allah be upon him), and he said: "As for Allah, the earth would indeed close upon one who is worse than him, but Allah wanted to inform you of your sanctity among yourselves."