A prostitute saw a dog moving around a well on a hot day and hanging out its tongue because of thirst. She drew water for it in her shoe and she was pardoned (for this act of hers).
Sahih Muslim Book 39, Hadith 211
← Previous Hadith A person suffered from intense thirst while on a journey, when he found a well. He climbed down into it and drank (water) and then came out and saw a dog lolling its tongue on account of thirst and eating the moistened earth. The person said: This dog has suffered from thirst as I had suffered from it. He climbed down into the well, filled his shoe with water, then caught it in his mouth until he climbed up and made the dog drink it. So Allah appreciated this act of his and pardoned him. Then (the Companions around him) said: Allah's Messenger, is there for us a reward even for (serving) such animals? He said: Yes, there is a reward for service to every living animal.

Sahih Muslim Book 39, Hadith 210 Next Hadith → There was a dog moving around a well whom thirst would have killed. Suddenly a prostitute from the prostitutes of Bani Isra'il happened to see it and she drew water in her shoe and made it drink, and she was pardoned because of this.

Sahih Muslim Book 39, Hadith 212