كتاب الإمارة
33  
The Book on Government
(26)
Chapter: The virtue of horses; "Goodness is tied to their Forelocks."
(26)
باب الْخَيْلُ فِي نَوَاصِيهَا الْخَيْرُ إِلَى يَوْمِ الْقِيَامَةِ ‏‏
Sahih Muslim 1871 a

It has been narrated on the authority of Ibn Umar that the Messenger of Allah (ﷺ) said:

There will be great benefit in the forelock of the horses until the Day of judgment.
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ الْخَيْلُ فِي نَوَاصِيهَا الْخَيْرُ إِلَى يَوْمِ الْقِيَامَةِ ‏"‏ ‏.‏
Reference : Sahih Muslim 1871a
In-book reference : Book 33, Hadith 141
USC-MSA web (English) reference : Book 20, Hadith 4612
  (deprecated numbering scheme)