It is narrated from Sayyiduna Safwan bin Assal (may Allah be pleased with him), who said: The Messenger of Allah (peace and blessings be upon him) sent me with an expedition and said: "Fight in the name of Allah, in the path of Allah. Do not steal from the spoils of war, do not act treacherously, and do not kill any child. And for the traveller, three days and their nights, and for the resident, one day and one night, of wiping over the leather socks (is the ruling)."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7366