Al-Zuhri (may Allah have mercy on him) narrates from Ibn Ka'b bin Malik (may Allah be pleased with him), who narrates from his uncle (may Allah be pleased with him), that when the Messenger of Allah (peace and blessings be upon him) sent him to Ibn Abi al-Huqayq, he forbade the killing of women and children.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18086