Hadith: The Prophet (may Allah's peace and blessings be upon him) arranged for a horse race among the horses that had been especially prepared for that purpose to take place between Al-Hafyā' and Thaniyyat al-Wadā‘.

عن عبد الله بن عمر رضي الله عنهما قال: «أَجْرَى النَّبِيُّ صلى الله عليه وسلم ما ضُمِّرَ مِن الْخَيْل: مِنْ الْحَفْيَاءِ إلَى ثَنِيَّةِ الوَداع، وَأَجْرَى ما لَمْ يُضَمَّرْ: مِنْ الثَّنِيَّةِ إلَى مسجد بني زُرَيْقٍ. قَال ابن عمر: وَكنْتُ فِيمَن أَجْرى. قَالَ سفيان: مِن الْحَفْيَاء إلى ثَنِيَّة الوداع: خمسة أمْيال، أو سِتَّة، ومن ثَنِيَّة الوداع إلى مسجد بني زُرَيْقٍ: مِيلٌ».
[صحيح] - [متفق عليه]

‘Abdullāh ibn ‘Umar (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) arranged for a horse race among the horses that had been especially prepared for that purpose to take place between Al-Hafyā' and Thaniyyat al-Wadā‘, and for the horses which had not been prepared from Thaniyyat al-Wadā‘ to the mosque of Banu Zurayq. Ibn ‘Umar said: "I was one of those who took part in that horse race." Sufyān, a sub-narrator, said: "The distance between Al-Hafyā' and Thaniyyat al-Wadā‘ is five or six miles, and between Thaniyyat al-Wadā‘ and the mosque of Banu Zurayq, there is one mile."
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

The Prophet (may Allah's peace and blessings be upon him) was ready for Jihad and thus observed what could help him undertake it. In this respect, he complied with Allah's saying: {And prepare against them whatever you are able of power and of stoods of war by which you may terrify the enemy of Allah and your enemy} [Al-Anfāl: 60]. So, he would keep horses under conditions that would make them strong. He would also train his Companions in horse racing in order for them to master the strategies of horse mounting. He also set the distance that trained and untrained horses should cover separately so that each category would receive proper training. In this regard, he made trained horses, which were strong enough because of their feeding system, race six miles. Untrained horses were made to run only one mile. ‘Abdullāh ibn ‘Umar (may Allah be pleased with him) was a young man then, and he participated in the horse race.