Musnad Ahmad 875:1

'Affan narrated to us, Jarir ibn Hazim narrated to us, he said: An old man sat with us in the place of Ayyub, and he heard the people talking, so he said: My master narrated to me, from the Messenger of Allah, may Allah bless him and grant him peace. I said: What is his name? He said: Qurrah ibn Da'mus al-Numayri. He said: I came to Medina and I came to the Messenger of Allah, may Allah bless him and grant him peace, and the people were around him. I began wanting to draw near to him, but I could not, so I called out to him: "O Messenger of Allah, ask forgiveness for the Numayri boy." He said: "May Allah forgive you." He said: The Messenger of Allah, may Allah bless him and grant him peace, sent al-Dahhak ibn Qays as a collector (of Zakat). When he returned, he returned with mature camels. The Messenger of Allah, may Allah bless him and grant him peace, said to him: "You went to Hilal ibn 'Amir, Numayr ibn 'Amir, and 'Amir ibn Rabi'ah, and you took the best of their wealth?" He said: "O Messenger of Allah, I heard you mentioning the military expedition, so I wanted to bring you camels for you to ride and to carry loads upon." He said: "By Allah, that which you left behind is more beloved to me than that which you took. Return them, and take their alms (Zakat) from the mediocre of their wealth." He said: So I heard the Muslims calling those camels—the mature ones—"the Mujahidat" (the ones for the struggle).