It is narrated from Sayyiduna al-Sa'ib bin Yazid (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) and Sayyiduna Abu Bakr (may Allah be pleased with him) did not appoint any judge, and the first to appoint a judge was Sayyiduna Umar (may Allah be pleased with him). He said to him: Keep the people from coming to me over petty disputes of a dirham or two.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6632