Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: We were with the Prophet (peace and blessings be upon him) on a journey, and I was riding a camel belonging to Sayyiduna Umar (may Allah be pleased with him). It was getting the better of me and would go ahead of all the people. Sayyiduna Umar (may Allah be pleased with him) would scold it and turn it back; then it would go ahead again, and Sayyiduna Umar (may Allah be pleased with him) would scold it and turn it back. The Prophet (peace and blessings be upon him) said: "O Umar! Sell it to me." He said: O Messenger of Allah! It is yours already. He (peace and blessings be upon him) said: "Sell it to me." So Sayyiduna Umar (may Allah be pleased with him) sold it to the Prophet (peace and blessings be upon him), and the Prophet (peace and blessings be upon him) said: "O Abdullah bin Umar! It is yours; do with it whatever you wish."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10702