Idmar (the preparation) of horses for racing
حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، حَدَّثَنَا اللَّيْثُ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ ـ رضى الله عنه أَنَّ النَّبِيَّ صلى الله عليه وسلم سَابَقَ بَيْنَ الْخَيْلِ الَّتِي لَمْ تُضَمَّرْ، وَكَانَ أَمَدُهَا مِنَ الثَّنِيَّةِ إِلَى مَسْجِدِ بَنِي زُرَيْقٍ. وَأَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ كَانَ سَابَقَ بِهَا. قَالَ أَبُو عَبْد اللَّهِ أَمَدًا غَايَةً فَطَالَ عَلَيْهِمْ الْأَمَدُ
Narrated `Abdullah: The Prophet (ﷺ) arranged for a horse race of the horses which had not been made lean; the area of the race was from Ath-Thaniya to the mosque of Bani Zuraiq. (The sub-narrator said, "`Abdullah bin `Umar was amongst those who participated in that horse race.").