Musnad Ahmad 27:1303

Husayn ibn Muhammad narrated to us, Sulayman ibn Qarm narrated to us, from Zayd—meaning Ibn Jubayr—from Nafi', from Ibn 'Umar, who said: The Messenger of Allah (may Allah bless him and grant him peace) passed by a slain woman during a military expedition he undertook. He forbade the killing of women and children.