Sahih Bukhari Volume 3, Book 46, Hadith 2467

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ سُمَىٍّ، مَوْلَى أَبِي بَكْرٍ عَنْ أَبِي صَالِحٍ السَّمَّانِ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ ‏"‏ بَيْنَا رَجُلٌ بِطَرِيقٍ، اشْتَدَّ عَلَيْهِ الْعَطَشُ فَوَجَدَ بِئْرًا فَنَزَلَ فِيهَا فَشَرِبَ، ثُمَّ خَرَجَ، فَإِذَا كَلْبٌ يَلْهَثُ يَأْكُلُ الثَّرَى مِنَ الْعَطَشِ، فَقَالَ الرَّجُلُ لَقَدْ بَلَغَ هَذَا الْكَلْبَ مِنَ الْعَطَشِ مِثْلُ الَّذِي كَانَ بَلَغَ مِنِّي، فَنَزَلَ الْبِئْرَ، فَمَلأَ خُفَّهُ مَاءً، فَسَقَى الْكَلْبَ، فَشَكَرَ اللَّهُ لَهُ، فَغَفَرَ لَهُ ‏"‏‏.‏ قَالُوا يَا رَسُولَ اللَّهِ وَإِنَّ لَنَا فِي الْبَهَائِمِ لأَجْرًا فَقَالَ ‏"‏ فِي كُلِّ ذَاتِ كَبِدٍ رَطْبَةٍ أَجْرٌ ‏"‏‏.‏

Narrated By Abu Huraira : The Prophet said, "A man felt very thirsty while he was on the way, there he came across a well. He went down the well, quenched his thirst and came out. Meanwhile he saw a dog panting and licking mud because of excessive thirst. He said to himself, "This dog is suffering from thirst as I did." So, he went down the well again and filled his shoe with water and watered it. Allah thanked him for that deed and forgave him. The people said, "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 (living being)."