Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings of Allah be upon him) used to observe i'tikaf during the middle ten days of Ramadan. So, he observed i'tikaf one year, until when the twenty-first night came—the night whose morning he (peace be upon him) would come out of his i'tikaf—he (peace be upon him) said: "Whoever has observed i'tikaf with us should also observe i'tikaf during the last ten (days)." And the complete hadith was narrated.