Musnad Abu Ya'la al-Mawsili 42:185

On the authority of Abu Salamah, he said: We discussed the Night of Decree (Laylat al-Qadr) among a group of Quraysh, so I went to Abu Sa’id al-Khudri, and he was a friend of mine. I said, "Will you not come out to the palm trees?" So he went out, and he was wearing a *khamisah* (a square-patterned garment). I said to him, "Did you hear the Messenger of Allah, may Allah bless him and grant him peace, mention the Night of Decree?" He said, "Yes. We performed *i’tikaf* (seclusion in the mosque) with the Messenger of Allah, may Allah bless him and grant him peace, during the middle ten days of Ramadan. We came out on the morning of the twentieth, and the Messenger of Allah, may Allah bless him and grant him peace, addressed us and said: 'I was shown the Night of Decree, but I forgot it, or I was made to forget it. So seek it in the last ten nights, in every odd-numbered night. And I saw that I was prostrating in water and mud. So whoever was performing *i’tikaf* with the Messenger of Allah, may Allah bless him and grant him peace, let him return.'" He continued: "So we returned, and we did not see a single patch of cloud in the sky. Then a cloud came, and it rained upon us until the mosque leaked—and it was made of palm fronds. The prayer was established, and I saw the Messenger of Allah, may Allah bless him and grant him peace, prostrating in the water and mud, until I saw the trace of the mud on his forehead."