It is narrated from Sayyiduna Suraqah bin Malik (may Allah be pleased with him) that he came to the Prophet (peace and blessings be upon him) during his illness and said: "Tell me, if a stray animal comes to the water-trough of my camels, will I have a reward if I give it water?" He (peace and blessings be upon him) said: "Yes, there is a reward in giving water to every creature with a thirsting liver."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6557