Musnad Ahmad 1114:1

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, Yazid ibn Abdullah ibn Qusayt narrated to me, from al-Qa'qa' ibn Abdullah ibn Abi Hadrad, from his father, Abdullah ibn Abi Hadrad, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) sent us to Idam. I went out with a group of Muslims, among whom were Abu Qatadah al-Harith ibn Rib'i and Muhallim ibn Jaththamah ibn Qays. We set out until, when we were in the valley of Idam, Amir al-Ashja'i passed by us on a young camel, having with him some small belongings and a skin of milk. When he passed by us, he greeted us with peace, but we withheld from him. Muhallim ibn Jaththamah attacked him and killed him because of something that had been between them, and he took his camel and his belongings. When we arrived at the Messenger of Allah (peace and blessings of Allah be upon him) and informed him of the news, the Quran was revealed concerning us: 'O you who have believed, when you go forth in the cause of Allah, investigate; and do not say to one who gives you [a greeting of] peace, "You are not a believer," aspiring for the goods of worldly life; for with Allah are many spoils. You [yourselves] were like that before; then Allah conferred His favor upon you, so investigate. Indeed Allah is ever, with what you do, Acquainted.'" [An-Nisa: 94]