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 woman in one of the battles, so he disapproved of it and forbade the killing of women and children.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6037
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ: 3014، م: 1744.