Muwatta Imam Malik (Riwayat Ibn al-Qasim)

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: “(Some) horses are a source of reward for a person, some are a means of protection, and some are a burden (sin) upon a person. The horses that are a source of reward are those which a person keeps ready in the way of Allah (for jihad), then he lets their reins loose in a field or garden, so as far as they graze in that place or garden, good deeds are written for him. And if they break their reins and climb one or two elevations, then for their footsteps and droppings, good deeds are written for that person. And if they pass by a stream and drink water from it, and their owner did not bring them there to give them water, even then good deeds are written for him, and this is a reward for him. The second person is the one who keeps them to fulfill his needs, to remain independent from others, and to avoid begging from others, and does not forget Allah’s right upon their necks and backs, then these are a protection for that person. And (the third) person who keeps horses out of pride, showing off, and enmity towards Muslims, then these are a sin for him.” The Prophet (peace and blessings be upon him) was asked about donkeys, so he said: “Nothing has been revealed to me regarding them except this comprehensive and unique verse: «فَمَن يَعْمَلْ مِثْقَالَ ذَرَّةٍ خَيْرًا يَرَهُ وَمَن يَعْمَلْ مِثْقَالَ ذَرَّةٍ شَرًّا يَرَهُ» So whoever does an atom’s weight of good will see it, and whoever does an atom’s weight of evil will see it.”

And with the same chain of narration, it is narrated from (Sayyiduna Ibn Umar, may Allah be pleased with them both) that the Messenger of Allah, peace and blessings be upon him, said: "Goodness has been written on the foreheads of horses until the Day of Resurrection."

And with the same chain of narration (from Sayyiduna Abdullah bin Umar, may Allah be pleased with him), it is narrated that the Messenger of Allah, peace and blessings be upon him, raced those horses which had been made lean and prepared for jihad from Hafyaa (a place) to Thaniyyat al-Wada' (another place), and those which had not been prepared were raced from Thaniyya to the mosque of Banu Zuraiq. And Abdullah bin Umar, may Allah be pleased with them both, was among those who participated in this competition.