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