Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrated from the Prophet (peace and blessings be upon him): "A man was passing along a road when he became thirsty. He went down into a well and drank water. When he came out, he saw a dog eating moist earth out of thirst. So the man went down into the well again, filled his leather sock with water and gave the dog to drink. Allah Almighty was so pleased with this deed of His servant that He forgave him." The Companions (may Allah be pleased with them) asked: "O Messenger of Allah, is there reward even in animals?" He (peace and blessings be upon him) said: "In every creature with a moist liver there is reward."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النفقات / 15818