The Messenger of Allah ﷺ used to spend the middle ten days of Ramadan in retirement and devotion (i'tikaf) in the mosque. One year he had retirement and devotion in the mosque (as usual); when the twenty-first night came, and this night when he used to come out his devotion in the mosque, he said: He who has engaged himself in devotion along with me should do so during the last ten days; I saw that night, that was caused to forget it, but I have seen myself prostrating in water and mud on the morning following (that night), so seek it in the last ten days and seek it every night with an odd number. Abu sa'id said: Rain fell that night, the mosque that was thatched building dripped, and my eyes saw the Messenger of Allah ﷺ with the traces of water and mud, on his forehead on the morning following the twenty-first night. (Using translation from Abū Dāʾūd 1382)   

أَنَّهُ قَالَ كَانَ رَسُولُ اللهِ ﷺ يَعْتَكِفُ الْعَشْرَ الْوَسَطَ مِنْ رَمَضَانَ فَاعْتَكَفَ عَامًا حَتَّى إِذَا كَانَ لَيْلَةُ إِحْدَى وَعِشْرِينَ وَهِيَ اللَّيْلَةُ الَّتِي يَخْرُجُ مِنْهَا مِنَ اعْتِكَافِهِ قَالَ مَنِ اعْتَكَفَ مَعِي فَلْيَعْتَكِفِ الْعَشْرَ الْأَوَاخِرَ وَقَدْ رَأَيْتُ هَذِهِ اللَّيْلَةَ ثُمَّ أُنْسِيتُهَا وَقَدْ رَأَيْتُنِي أَسْجُدُ صَبِيحَتَهَا فِي مَاءٍ وَطِينٍ فَالْتَمِسُوهَا فِي الْعَشْرِ الْأَوَاخِرِ وَالْتَمِسُوهَا فِي كُلِّ وِتْرٍ قَالَ أَبُو سَعِيدٍ فَمَطَرَتْ تِلْكَ اللَّيْلَةُ وَكَانَ الْمَسْجِدُ عَلَى عَرِيشٍ فَوُكِفَ الْمَسْجِدُ قَالَ أَبُو سَعِيدٍ فَأَبْصَرَتْ عَيْنَايَ رَسُولَ اللهِ ﷺ وَعَلَى جَبْهَتِهِ وَأَنْفِهِ أَثَرُ الْمَاءِ وَالطِّينِ صَبِيحَةَ إِحْدَى وَعِشْرِينَ