Abu Saeed Khudri reported,

The Messenger of Allah ﷺ used to perform itikaf during the middle ten days of Ramadan. When the evening of the twentieth night came, with twenty nights having passed and the twenty-first about to begin, he would return to his dwelling, and those who had been performing itikaf with him would also return.One year, however, during the month in which he was performing itikaf, he stayed through the night on which he would normally return home. Those who had been with him went back as usual. He then addressed the people, instructing them as Allah willed, and said, "I used to perform itikaf during these ten days, but it has now occurred to me to perform itikaf during these last ten. So whoever was in itikaf with me, let him remain in his place of itikaf. I was shown this night, then I was made to forget it. So seek it in the last ten, and seek it on every odd night. I have seen myself prostrating in water and mud."That very night, the sky poured down rain, and the roof of the mosque leaked at the spot where the Prophet ﷺ prayed, on the night of the twenty-first. My own eyes saw the Messenger of Allah ﷺ, and I looked at him as he finished the dawn prayer, his face covered with mud and water.

عن أبي سعيد الخدري قال

كان رسول الله ﷺ يجاور في رمضان العشر التي في وسط الشهر فإذا كان حين يمسي من عشرين ليلة تمضي ويستقبل إحدى وعشرين رجع إلى مسكنه يجاور معه وأنه أقام في شهر جاور فيه الليلة التي كان يرجع ورجع من كان فيها فخطب الناس فأمرهم ما شاء الله ثم قال: كنت أجاور هذه العشر، ثم قد بدا لي أن أجاور هذه العشر الأواخر. فمن كان اعتكف معي فليثبت في معتكفه وقد أريت هذه الليلة ثم أنسيتها فابتغوها في العشر الأواخر، وابتغوها في كل وتر، وقد رأيتني أسجد في ماء وطين. فاستهلت السماء في تلك الليلة فأمطرت فوكف المسجد في مصلى النبي ﷺ ليلة إحدى وعشرين فبصرت عيني رسول الله ﷺ ونظرت إليه انصرف من الصبح ووجهه ممتلئ طينا وماء.