Sunan an-Nasa'i, Volume 2, Book 12, Hadith 1125 (DarusSalam) ⓘ

'Aishah said: "I noticed that the Messenger of Allah was missing from bed, so I started to look for him, and I thought that he had gone to one of his concubines. Then my hand fell on him when he was prostrating and saying: "Allahummaghfirli ma asrartu wa ma a'lant (O Allah, forgive me for what (sin) I have concealed and what I have done openly).'"

أَخْبَرَنَا مُحَمَّدُ بْنُ قُدَامَةَ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ هِلاَلِ بْنِ يِسَافٍ، قَالَ قَالَتْ عَائِشَةُ رضى الله عنها فَقَدْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم مِنْ مَضْجَعِهِ فَجَعَلْتُ أَلْتَمِسُهُ وَظَنَنْتُ أَنَّهُ أَتَى بَعْضَ جَوَارِيهِ فَوَقَعَتْ يَدِي عَلَيْهِ وَهُوَ سَاجِدٌ وَهُوَ يَقُولُ ‏ "‏ اللَّهُمَّ اغْفِرْ لِي مَا أَسْرَرْتُ وَمَا أَعْلَنْتُ ‏" ‏ ‏.‏