Musnad Ahmad 333:33

Yahya ibn Sa'id narrated to us, from Yazid ibn Abi 'Ubayd, who said: Salamah ibn al-Akwa' narrated to us, saying: We went out with the Prophet, peace and blessings of Allah be upon him, to Khaybar. A man from the people said: "O 'Amir, if only you would let us hear some of your rhythmic verses (hiniyyat)." He said: So he dismounted and began to chant for them, mentioning: "By Allah, were it not for Allah, we would not have been guided, Nor would we have given charity, nor would we have prayed." He mentioned other poetry besides this, but I did not memorize it. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Who is this driver?" They said: "'Amir ibn al-Akwa'." He said: "May Allah have mercy on him." A man from the people said: "O Prophet of Allah, if only you had let us enjoy him (longer)." When the people met (in battle), they fought them, and 'Amir ibn al-Akwa' was struck by the hilt of his own sword and died. When evening came, they lit many fires. The Messenger of Allah, peace and blessings of Allah be upon him, said: "What is this fire? What is being cooked upon it?" They said: "Domestic donkeys." He said: "Spill out what is in them and break them." A man said: "Shall we not spill out what is in them and wash them?" He said: "Or that."