Sunan an Nasai
The Book of Horses, Races and Shooting
Hadith #13
28.13
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ " الْخَيْلُ فِي نَوَاصِيهَا الْخَيْرُ إِلَى يَوْمِ الْقِيَامَةِ " .
It was narrated from Ibn 'Umar that the Prophet said:"There is goodness in the forelocks of horses until the Day of Resurrection