وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ سُمَىٍّ، مَوْلَى أَبِي بَكْرٍ عَنْ أَبِي صَالِحٍ السَّمَّانِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ بَيْنَمَا رَجُلٌ يَمْشِي بِطَرِيقٍ إِذِ اشْتَدَّ عَلَيْهِ الْعَطَشُ فَوَجَدَ بِئْرًا فَنَزَلَ فِيهَا فَشَرِبَ وَخَرَجَ فَإِذَا كَلْبٌ يَلْهَثُ يَأْكُلُ الثَّرَى مِنَ الْعَطَشِ فَقَالَ الرَّجُلُ لَقَدْ بَلَغَ هَذَا الْكَلْبَ مِنَ الْعَطَشِ مِثْلُ الَّذِي بَلَغَ مِنِّي فَنَزَلَ الْبِئْرَ فَمَلأَ خُفَّهُ ثُمَّ أَمْسَكَهُ بِفِيهِ حَتَّى رَقِيَ فَسَقَى الْكَلْبَ فَشَكَرَ اللَّهُ لَهُ فَغَفَرَ لَهُ ‏"‏ ‏.‏ فَقَالُوا يَا رَسُولَ اللَّهِ وَإِنَّ لَنَا فِي الْبَهَائِمِ لأَجْرًا فَقَالَ ‏"‏ فِي كُلِّ ذَاتِ كَبِدٍ رَطْبَةٍ أَجْرٌ ‏"‏ ‏.‏

Yahya related to me from Malik from Sumayy, the mawla of Abu Bakrfrom Abu Salih as-Samman from Abu Hurayra that the Messenger of Allah,may Allah bless him and grant him peace, said, "A man was walking on aroad when he became very thirsty. He found a well and went into it anddrank and came out. There was a dog panting and eating earth out ofthirst. The man said, 'This dog has become as thirsty as I was.' Hewent down into the well and filled his shoe and then held it in hismouth until he climbed out and gave the dog water to drink. Allahthanked him for it and forgave him." They said, "Messenger of Allah,do we have a reward for taking care of beasts?" He said, "There is areward for every one with a moist liver." Translation Not Available

Book Ref: Muwatta Imam Malik Book 49 Hadith 1696
Web Ref:  Muwatta Imam Malik Book 49 Hadith 23