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
Abdullah bin Umar (may Allah be pleased with them both) said that in one of the campaigns of the Messenger of Allah (peace and blessings be upon him) a woman was found killed, so he (peace and blessings be upon him) disapproved of the killing of women and children.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18087
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that a woman was found killed in one of the campaigns, so the Messenger of Allah (peace and blessings be upon him) forbade the killing of women and children.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18088
Sayyiduna al-Aswad bin Sari' (may Allah be pleased with him) said: I went on a campaign together with the Messenger of Allah (peace and blessings be upon him). We were granted victory, and the people went on killing until they even killed the children. When the Messenger of Allah (peace and blessings be upon him) learned of this, he (peace and blessings be upon him) said: "What is the matter with people that killing carried them so far that they even killed the children?" A man said: O Messenger of Allah, they are the children of the polytheists. He (peace and blessings be upon him) said: "Are not the best of you the sons of the polytheists?" Then he said: "Do not kill children," and he (peace and blessings be upon him) said it three times. Then he said: "Every child is born upon the fitrah (natural disposition) until its tongue becomes articulate; then its parents make it a Jew or a Christian."
(b) Abu Ja'far Ahmad bin Ubayd (may Allah have mercy on him) said: The meaning of his saying "Every soul is born upon the fitrah" is the fitrah they had when they were brought out from the loins of Adam (peace be upon him) and affirmed the Oneness of Allah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18089