Sunan an-Nasa'i, Hadith 3576 ⓘ
It was narrated that 'Urwah said that he heard the Messenger of Allah say: "Goodness is tied to the forelocks of horses until the Day of Resurrection: Reward and spoils of war."
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ أَنْبَأَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، قَالَ أَنْبَأَنَا شُعْبَةُ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي السَّفَرِ، عَنِ الشَّعْبِيِّ، عَنْ عُرْوَةَ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " الْخَيْلُ مَعْقُودٌ فِي نَوَاصِيهَا الْخَيْرُ إِلَى يَوْمِ الْقِيَامَةِ الأَجْرُ وَالْمَغْنَمُ " .
also referenced under: Book 28, Hadith 16 (In-Book) & Volume 4, Book 28, Hadith 3606 (DarusSalam)