Sahih Bukhari Volume 3, Book 42, Hadith 2364

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ سُمَىٍّ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ بَيْنَا رَجُلٌ يَمْشِي فَاشْتَدَّ عَلَيْهِ الْعَطَشُ، فَنَزَلَ بِئْرًا فَشَرِبَ مِنْهَا، ثُمَّ خَرَجَ فَإِذَا هُوَ بِكَلْبٍ يَلْهَثُ، يَأْكُلُ الثَّرَى مِنَ الْعَطَشِ، فَقَالَ لَقَدْ بَلَغَ هَذَا مِثْلُ الَّذِي بَلَغَ بِي فَمَلأَ خُفَّهُ ثُمَّ أَمْسَكَهُ بِفِيهِ، ثُمَّ رَقِيَ، فَسَقَى الْكَلْبَ فَشَكَرَ اللَّهُ لَهُ، فَغَفَرَ لَهُ ‏"‏‏.‏ قَالُوا يَا رَسُولَ اللَّهِ، وَإِنَّ لَنَا فِي الْبَهَائِمِ أَجْرًا قَالَ ‏"‏ فِي كُلِّ كَبِدٍ رَطْبَةٍ أَجْرٌ ‏"‏‏.‏ تَابَعَهُ حَمَّادُ بْنُ سَلَمَةَ وَالرَّبِيعُ بْنُ مُسْلِمٍ عَنْ مُحَمَّدِ بْنِ زِيَادٍ‏.‏

Narrated By Abu Huraira : Allah's Apostle said, "While a man was walking he felt thirsty and went down a well and drank water from it. On coming out of it, he saw a dog panting and eating mud because of excessive thirst. The man said, 'This (dog) is suffering from the same problem as that of mine. So he (went down the well), filled his shoe with water, caught hold of it with his teeth and climbed up and watered the dog. Allah thanked him for his (good) deed and forgave him." The people asked, "O Allah's Apostle! Is there a reward for us in serving (the) animals?" He replied, "Yes, there is a reward for serving any animate."