Sunan an-Nasa'i 3582
سنن النسائي#3582SahihIt was narrated from Abu Hurairah that the Messenger of Allah said:"Whoever keeps a horse for the cause of Allah out of faith in Allah and believing the promise of Allah, its feed, water, urine and dung will all count as Hasanat in the balance of his deeds
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih Bukhari
In-book reference: 28:22