Sayyiduna Rabah bin al-Rabi' (may Allah be pleased with him) said: We were with the Messenger of Allah (peace and blessings be upon him) on a military expedition, and Khalid bin al-Walid was in command of the vanguard (the forward detachment) of the people. Then we saw a woman lying slain on the road; the people were marvelling at her physique, and it was the vanguard that had killed her. The Messenger of Allah (peace and blessings be upon him) came, stood over her, and then said to a man: "Go to Khalid bin al-Walid and tell him that he must never kill any child or hired labourer."
Hadith Referenceالمعجم الكبير للطبراني / باب الراء / 4605