Musnad Ahmad 523:2

Waki’ narrated to us, Sufyan narrated to us, from Abu al-Zinad, from al-Muraqqa’ ibn Sayfi, from Hanzala al-Katib, who said: We went on a military expedition with the Prophet, peace and blessings of Allah be upon him, and we passed by a slain woman, and the people had gathered around her. He said: So they cleared a path for him. He said: "This one was not fighting." Then he said to a man: "Go to Khalid ibn al-Walid and say to him: 'The Messenger of Allah, peace and blessings of Allah be upon him, commands you not to kill offspring nor a hired laborer.'"