Musannaf Ibn Abi Shayba 33:486

Abdullah ibn Numayr narrated to us, from al-A’mash, from Abu Yahya, the freed slave of Ja’dah ibn Hubayrah, from Abu Hurayrah, who said: A man passed by a dog lying down near a well, having almost died of thirst. He did not find anything to give it water in, so he took off his leather sock and began to scoop [water] for it and give it to drink. Allah accounted for it for him, so He entered him into Paradise.