Musnad Ahmad Hadith 10699

It is narrated from Abu Hurairah (may Allah be pleased with him) that the Holy Prophet (ﷺ) said: A man was walking on the road when he was overcome by intense thirst. He found a well nearby, so he went down into the well, quenched his thirst, and came out. Suddenly, he saw a dog that was licking mud out of thirst. He thought to himself that this dog must be as thirsty as I was. So he went down into the well again, filled his sock with water, held it in his mouth, came out, and gave the dog water to drink. Allah appreciated this deed of his and forgave him. When the companions (may Allah be pleased with them) heard this, they asked, "O Messenger of Allah (ﷺ), is there a reward for us even in (doing good to) animals?" The Holy Prophet (ﷺ) replied, "There is a reward in (doing good to) every living being with a moist liver."