It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) saw a slain person in one of the battles, so he expressed disapproval and forbade the killing of women and children.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6055
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ: 301، م: 1744.