Sahih al-Bukhari 3119
Sahih al-Bukhari · Book 57: One-fifth of Booty to the Cause of Allah (Khumus) · The statement of the Prophet ﷺ: "Booty has been made legal for you Muslims."
Narrated `Urwa-al-Bariqi:
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 " .
The Prophet (ﷺ) said, "Horses are always the source of good, namely, rewards (in the Hereafter) and booty, till the Day of Resurrection."