Sahih Adab al-Mufrad

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "A man was walking along the road when he felt extremely thirsty. He found a well, so he went down into it and drank water. When he came out, he saw a dog panting and licking the wet earth out of thirst. The man said, 'This dog is suffering from thirst just as I was.' So he went down into the well again, filled his shoe with water, held it in his mouth, and climbed up, then gave the dog water to drink. Allah appreciated this deed of his and forgave him." The people asked, "O Messenger of Allah! Is there a reward for us in (doing good to) animals as well?" He replied, "There is a reward for (doing good to) every living being."

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "A woman was punished because of a cat which she had tied up, until it died of hunger and thirst. She entered Hell because of that cat. It will be said to her (and Allah knows best): When you kept it tied up, you neither fed it nor gave it water, nor did you let it go free so that it could eat the insects of the earth."

Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with him) narrates from the Prophet (peace and blessings of Allah be upon him) that he said: "Show mercy, you will be shown mercy. Forgive, Allah will forgive you. Destruction is for those who hear something and ignore it, destruction is for those who persist in sins, those who stubbornly persist in their committed sins even though they know that it is unlawful."

It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him), he said that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever shows mercy to anyone, even to an animal to be slaughtered, Allah will show mercy to him on the Day of Resurrection."