Musnad Abu Ya'la al-Mawsili 2:119

Ahmad ibn Ibrahim narrated to us, Bishr narrated to us, from al-Awza'i, from Yahya ibn Abi Kathir, from Abu Salamah, from Abu Hurayrah, who said: While Umar ibn al-Khattab was addressing the people on Friday, Uthman ibn Affan entered the mosque. Umar alluded to him and said, "What is the matter with men who arrive late after the call?" Uthman said, "O Commander of the Faithful, I did nothing more when I heard the call than perform ablution, then I came." Umar said, "And ablution as well? Did you not hear the Messenger of Allah, peace and blessings of Allah be upon him, say: 'When one of you comes to Friday [prayer], let him perform ghusl (full ritual bath)'?"