Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) used to observe i'tikaf during the middle ten days of Ramadan. One year, he observed i'tikaf until when the twenty-first night came—which was the night after which he was to return from the place of i'tikaf—the Prophet (peace and blessings be upon him) said: Whoever has observed i'tikaf with me should also observe i'tikaf during the last ten days, for I was shown that night, but then it was made to be forgotten by me. I saw myself prostrating in water and mud on the morning of that night, so seek it in the last ten nights, seek it in every odd night. Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrates: That very night it rained. The roof of the mosque was made of palm leaves and it started to leak. Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) used to say: I saw with my own eyes the Prophet (peace and blessings be upon him), when he turned towards us after praying, there was a mark of water and mud on his blessed forehead and blessed nose. This was the morning of the twenty-first night.