Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "May Allah have mercy on my brother Abdullah bin Rawahah; wherever the time of prayer came upon him, he would make his mount kneel (and pray)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13184