The Messenger of Allah ﷺ trained horses for racing by reducing their feed. He would send the lean, trained horses to race from al-Hafya to Thaniyyat al-Wada, and the untrained ones from Thaniyyat al-Wada to the mosque of Banu Zurayq.
حدثنا علي بن محمد حدثنا عبد الله بن نمير عن عبيد الله عن نافع
ضمر رسول الله ﷺ الخيل فكان يرسل التي ضمرت من الحفياء إلى ثنية الوداع والتي لم تضمر من ثنية الوداع إلى مسجد بني زريق
Muslim narrated it in the Book of Leadership, in the chapter on horse racing and conditioning horses for it, hadith no. 1870, from the hadith of Ibn Numayr, in this manner.