Sayyiduna Rabah bin Rabi' (may Allah be pleased with him) said: We were with the Messenger of Allah (peace and blessings be upon him) on a campaign. He (peace and blessings be upon him) saw people gathered around something, so he (peace and blessings be upon him) sent a man, saying: "See what these people are gathered around." He came back and said that they were gathered around a woman who had been killed. He (peace and blessings be upon him) said: "This woman was not one who would fight." The narrator said: Sayyiduna Khalid bin al-Walid (may Allah be pleased with him) was in charge of the vanguard. He (peace and blessings be upon him) sent someone and said: "Tell Khalid not to kill any woman or hired worker."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18104