Zadhan narrated that a man asked Ali (may Allah be pleased with him) about ghusl (ritual bath), so he replied, "If you wish, perform ghusl every day." The man asked, "The ghusl that is obligatory?" Ali (may Allah be pleased with him) replied, "On the day of Jumu'ah (Friday), the day of Arafah, the day of sacrifice (Eid al-Adha), and the day of Eid al-Fitr."
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 988