Musa bin Abi Muslim relates that he asked Ibn Umar (may Allah be pleased with them both) about stopping at al-Muhassab, and he said: "It is a Sunnah; the Messenger of Allah (peace and blessings be upon him), Abu Bakr and Umar (may Allah be pleased with them both) made their mounts kneel there."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13268