(a) Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) was delivering the sermon to the people on Friday when Sayyiduna Uthman bin Affan (may Allah be pleased with him) entered the mosque. Sayyiduna Umar (may Allah be pleased with him), addressing him, said: "What is the matter with men who come after the call to prayer?" Sayyiduna Uthman (may Allah be pleased with him) said: "O Commander of the Believers! When I heard the call to prayer, I only performed ablution and came to the mosque." Sayyiduna Umar (may Allah be pleased with him) said: "Only ablution? Did you not hear the Messenger of Allah (peace and blessings be upon him) saying: 'When anyone comes to the Friday prayer, let him take a ritual bath'?" (b) Imam al-Shafi'i (may Allah have mercy on him) said: Sayyiduna Uthman (may Allah be pleased with him) did not abandon the prayer for the sake of the ritual bath, and Sayyiduna Umar (may Allah be pleased with him) did not order him to go out to take the bath; this is evidence that both of them knew that the order of the Messenger of Allah (peace and blessings be upon him) was optional.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1405