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 middle ten days of Ramadan in one year, until the twenty-first night came, the night when he (peace be upon him) was to come out of i'tikaf. He (peace be upon him) delivered a sermon and said: "Those who sat in i'tikaf with me (should return and) observe i'tikaf for the last ten days as well." And he said: "Laylat al-Qadr was shown to me (in a dream), then it was made to be forgotten. I saw in my dream as if I was prostrating in mud in the morning. So seek Laylat al-Qadr in the last ten nights, and seek it in the odd nights." Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) says that on that very night it rained, and the roof of the mosque was made of palm branches, so it started to leak. Abu Sa'id (may Allah be pleased with him) says: I myself saw with my own eyes that on the morning of the twenty-first, there was mud on the forehead and nose of the Messenger of Allah (peace and blessings be upon him).
Hadith Referenceالسنن المأثورة / باب ما جاء في الاعتكاف / 348
Hadith Takhrijصحیح بخاری، الاعتکاف باب الاعتکاف فی العشر الأواخر الخ ، رقم : 2027 ، صحیح مسلم، الصیام، باب فضل لیلۃ القدر، رقم : 1167