Musnad Ahmad 512:4

Yazid ibn Harun narrated to us, Muhammad ibn Ishaq informed us, from al-Zuhri, from Abd al-Rahman ibn Malik ibn Ju'shum, from his father, from his uncle Suraqah ibn Malik ibn Ju'shum, who said: I asked the Messenger of Allah, peace and blessings of Allah be upon him, about a stray camel that comes to my watering troughs which I have prepared for my camels: "Do I have a reward in the matter of giving it water?" He said: "Yes, in every living creature with a burning liver [i.e., a thirsty living being], there is a reward."