Abbad bin Abdullah bin al-Zubayr (may Allah have mercy on him) said: We performed Hajj with Sayyiduna Mu'awiyah (may Allah be pleased with him) in the year he performed Hajj, and he prayed Zuhr as two rak'ahs. Then Marwan bin al-Hakam and Amr bin Uthman came in to him and said: "What is this prayer?" He said: "This is the Sunnah; I prayed it with the Messenger of Allah (peace and blessings be upon him), and with Sayyiduna Abu Bakr and Sayyiduna Umar (may Allah be pleased with them both)." They said: "Your cousin used to complete it as four rak'ahs." He said: "This is all I remember."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16814