Ibn Awn (may Allah have mercy on him) said: I wrote to Nafi' (may Allah have mercy on him) asking about inviting (to Islam) before fighting. He replied: That invitation was only in the early period of Islam. the Messenger of Allah (peace and blessings be upon him) made a surprise raid on Banu al-Mustaliq while they were unaware (of the attack), and their animals were being watered. He (peace and blessings be upon him) killed their fighters and took their children captive, and on that day Sayyidah Juwayriyah bint al-Harith (may Allah be pleased with her) came to him (peace and blessings be upon him). Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrated this to me, and he was in that army.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18023