Sayyiduna Buraydah (may Allah be pleased with him) says: The Prophet (peace and blessings be upon him) had horses trained and fixed a specific time for their training. Then he said: "On such and such a day, at such and such a place (their race will be held)." And for the horses that had not been trained, the limit of their race was shorter than that.
Imam al-Bazzar recorded it. Its chain contains a narrator, Salih bin Hibban, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجهاد / 9361