Lu'lu' wal-Marjan

Narrated Abu Huraira (may Allah be pleased with him): The Messenger of Allah (peace and blessings of Allah be upon him) said: A man was walking when he felt severe thirst. He went down into a well and drank water. When he came out, he saw a dog panting and licking mud because of thirst. He said (to himself): This dog is suffering from thirst just as I was. (So he went down into the well again,) filled his leather sock with water, held it in his mouth, and climbed up, then gave the dog water to drink. Allah accepted this deed of his and forgave him. The Companions (may Allah be pleased with them) asked: O Messenger of Allah! Is there a reward for us in (serving) animals as well? He (peace and blessings of Allah be upon him) said: There is a reward for serving every living being.

Hazrat Abu Huraira (may Allah be pleased with him) narrated that the Noble Prophet (peace and blessings be upon him) said: A dog was circling around a well, as if it was about to die from extreme thirst, when a woman from the Children of Israel, who was a prostitute, saw it. She took off her shoe and gave water to the dog to drink, and she was forgiven because of that (action).