It is narrated from Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) observed i'tikaf during the first ten days of Ramadan, then he observed i'tikaf during the middle ten days in a Turkish tent, at the door of which a piece of mat was hanging. Then he narrated the complete hadith. I have already written this hadith before.