Sahih al-Bukhari, Volume 4, Book 52, Hadith 102 (USC-MSA) ⓘ
Narrated `Abdullah bin `Umar: Allah's Messenger said, "Good will remain (as a permanent quality) in the foreheads of horses till the Day of Resurrection."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْخَيْلُ فِي نَوَاصِيهَا الْخَيْرُ إِلَى يَوْمِ الْقِيَامَةِ " .
also referenced under: Book 56, Hadith 65 (In-Book) & Hadith 2849 (DarusSalam)