Abu Salamah bin Abd al-Rahman (may Allah have mercy on him) narrates: We were discussing Laylat al-Qadr among a group of Quraysh, so I got up and went to Abu Sa'id al-Khudri (may Allah be pleased with him) and said: O Abu Sa'id! Will you not come out with us to the palm grove? He said: Yes. He called for a striped woollen cloak and wrapped it around himself, and we went out. I said: Did you hear the Messenger of Allah (peace and blessings be upon him) mention Laylat al-Qadr? He said: Yes. We performed i'tikaf with the Messenger of Allah (peace and blessings be upon him) in the middle ten days of Ramadan. On the morning of the twentieth of Ramadan he stood among us and said: "Whoever has gone out, let him return, for I was shown Laylat al-Qadr and then forgot it, so seek it in the odd nights of the last ten. And I was shown that I was prostrating in water and mud." We could not see a single wisp of cloud in the sky. Then the iqamah for the prayer was called, a cloud rose up, and rain fell on us until the roof of the mosque streamed, and their roof in those days was made of palm branches. I saw the Messenger of Allah (peace and blessings be upon him) prostrating in mud and water, until I saw the trace of mud on the tip of his nose and on his forehead.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8591