It is narrated from Abdullah bin Awn that Nafi' (may Allah have mercy on him) wrote to him and informed him that Ibn Umar (may Allah be pleased with them both) informed that when the Prophet ﷺ attacked Banu al-Mustaliq, they were completely unaware, with their animals at the place of Muraysi'. The Prophet ﷺ killed their fighting men and took the women and children captive.
Hadith Referenceمسند الإمام الشافعي / كتاب الجهاد وقسم الغنائم / 1741
Hadith Takhrijاخرجه البخاري، العتق ، باب من ملك من العرب رقيقا فوهب...... الخ (2541) ومسلم، الجهاد والسير، باب جواز الاغارة على الكفار اللذين...... الخ (1730)۔