Abu Salama reported

'We discussed amongst ourselves Lailat-ul-Qadr. I came to Abu Sa'id al-Khudri (Allah be pleased with him) who was a friend of mine and said to him: Would you not go with us to the garden of date trees? He went out with a cloak over him. I said to him: Did you hear the Messenger of Allah (ﷺ) making mention of Lailat-ul-Qadr? He said: Yes, (and added) we were observing i'tikaf with the Messenger of Allah (ﷺ) in the middle ten days of Ramadan, and came out on the morning of the twentieth and the Messenger of Allah (ﷺ) addressed us and said: I was shown Lailat-ul-Qadr, but I forgot (the exact night) or I was caused to forget it, so seek it in the last ten odd (nights), and I was shown that I was prostrating in water and clay. So he who wanted to observe i'tikaf with the Messenger of Allah (ﷺ) should return (to the place of i'tikaf). He (Abu Sa'id al-Khudri) said: And we returned and did not find any patch of cloud in the sky. Then the cloud gathered and there was (so heavy) a downpour that the roof of the mosque which was made of the branches of date-palms began to drip. Then there was prayer and I saw the Messenger of Allah (ﷺ) prostrating in water and clay till I saw the traces of clay on his forehead.