Musnad Ahmad 27:675

Isma'il narrated to us, from Ibn 'Awn, who said: I wrote to Nafi' asking him about the supplication at the time of fighting. He wrote back to me: "That was only in the beginning of Islam. The Prophet of Allah (may Allah bless him and grant him peace) raided the Banu al-Mustaliq while they were unaware and their livestock were being watered at the water source. He killed their fighting men, took their offspring captive, and on that day he acquired Juwayriyah bint al-Harith." 'Abdullah narrated that to me, and he was in that army.