Sahih al-Bukhari, Volume 4, Book 53, Hadith 348 (USC-MSA) ⓘ
Narrated `Urwa-al-Bariqi: The Prophet said, "Horses are always the source of good, namely, rewards (in the Hereafter) and booty, till the Day of Resurrection."
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا خَالِدٌ، حَدَّثَنَا حُصَيْنٌ، عَنْ عَامِرٍ، عَنْ عُرْوَةَ الْبَارِقِيِّ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الْخَيْلُ مَعْقُودٌ فِي نَوَاصِيهَا الْخَيْرُ الأَجْرُ وَالْمَغْنَمُ إِلَى يَوْمِ الْقِيَامَةِ " .
also referenced under: Book 57, Hadith 28 (In-Book) & Hadith 3119 (DarusSalam)