أَخْبَرَنَا مُحَمَّدُ بْنُ سَلَمَةَ، وَالْحَارِثُ بْنُ مِسْكِينٍ، قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ، - وَاللَّفْظُ لَهُ - عَنِ ابْنِ الْقَاسِمِ، قَالَ حَدَّثَنِي مَالِكٌ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَبِي صَالِحٍ السَّمَّانِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ الْخَيْلُ لِرَجُلٍ أَجْرٌ وَلِرَجُلٍ سَتْرٌ وَعَلَى رَجُلٍ وِزْرٌ فَأَمَّا الَّذِي هِيَ لَهُ أَجْرٌ فَرَجُلٌ رَبَطَهَا فِي سَبِيلِ اللَّهِ فَأَطَالَ لَهَا فِي مَرْجٍ أَوْ رَوْضَةٍ فَمَا أَصَابَتْ فِي طِيَلِهَا ذَلِكَ فِي الْمَرْجِ أَوِ الرَّوْضَةِ كَانَ لَهُ حَسَنَاتٌ وَلَوْ أَنَّهَا قَطَعَتْ طِيَلَهَا ذَلِكَ فَاسْتَنَّتْ شَرَفًا أَوْ شَرَفَيْنِ كَانَتْ آثَارُهَا ‏"‏ ‏.‏ وَفِي حَدِيثِ الْحَارِثِ ‏"‏ وَأَرْوَاثُهَا حَسَنَاتٍ لَهُ وَلَوْ أَنَّهَا مَرَّتْ بِنَهَرٍ فَشَرِبَتْ مِنْهُ وَلَمْ يُرِدْ أَنْ تُسْقَى كَانَ ذَلِكَ حَسَنَاتٍ فَهِيَ لَهُ أَجْرٌ وَرَجُلٌ رَبَطَهَا تَغَنِّيًا وَتَعَفُّفًا وَلَمْ يَنْسَ حَقَّ اللَّهِ عَزَّ وَجَلَّ فِي رِقَابِهَا وَلاَ ظُهُورِهَا فَهِيَ لِذَلِكَ سَتْرٌ وَرَجُلٌ رَبَطَهَا فَخْرًا وَرِيَاءً وَنِوَاءً لأَهْلِ الإِسْلاَمِ فَهِيَ عَلَى ذَلِكَ وِزْرٌ ‏"‏ ‏.‏ وَسُئِلَ النَّبِيُّ صلى الله عليه وسلم عَنِ الْحَمِيرِ فَقَالَ ‏"‏ لَمْ يَنْزِلْ عَلَىَّ فِيهَا شَىْءٌ إِلاَّ هَذِهِ الآيَةُ الْجَامِعَةُ الْفَاذَّةُ ‏{‏ فَمَنْ يَعْمَلْ مِثْقَالَ ذَرَّةٍ خَيْرًا يَرَهُ * وَمَنْ يَعْمَلْ مِثْقَالَ ذَرَّةٍ شَرًّا يَرَهُ ‏}‏ ‏"‏ ‏.‏

It was narrated from Abu Hurairah that the Messenger of Allah said: "Horses may bring reward to a man, or they may be a means of protection, or they may be a burden (of sin). As for that which brings reward, it is a man who keeps it for the cause of Allah and ties it with a long rope in a pasture or a garden; whatever it eats or drinks in that pasture or garden will count as good deeds for him. If it breaks its rope and jumps over one or two hills, its footsteps" -and according to the Hadith of Al-Harith, "its dung will count as good deeds for him. If it passes by a river and drinks from it, even though (its owner) did not intend to give it water from that river, that will also bring him reward. If a man keeps a horse in order to earn an independent living and avoid asking others for help, and he does not forget his duty toward Allah with regard to their (the horses') necks and backs, then they will be a means of protection for him. If a man keeps horses out of pride, to show off before others and to fight the Muslims, then that will be a burden (of sin) for him." The Prophet was asked about donkeys and he said: "Nothing has been revealed to me concerning them except this Verse which is comprehensive in meaning: 'So whosoever does good equal to the weight of an atom (or a small ant) shall see it. And whosoever does evil equal to the weight of an atom (or a small ant) shall see it.'" Translation Not Available

Book reference: Sunan An Nisai Book 28 Hadith 3563
Web reference: Sunan An Nisai Volume 4 Book 28 Hadith 3593