It was narrated from 'Abdah bin Abi Lubabah that Ibn Yasaf told him that he asked 'Aishah, the wife of the Prophet (ﷺ) , : What supplication did the Messenger of Allah (ﷺ) say the most before he died? She said: "The supplication that he said the most was: 'Allahumma, inni a'udhu bika min sharri ma 'amiltu wa min sharri ma lam a'mal ba'd (O Allah, I seek refuge with You from the evil of what I have done, and from the evil of what I have not done yet.)'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا يُونُسُ بْنُ عَبْدِ الأَعْلَى، عَنِ ابْنِ وَهْبٍ، قَالَ أَخْبَرَنِي مُوسَى بْنُ شَيْبَةَ، عَنِ الأَوْزَاعِيِّ، عَنْ عَبْدَةَ بْنِ أَبِي لُبَابَةَ، أَنَّ ابْنَ يِسَافٍ، حَدَّثَهُ أَنَّهُ، سَأَلَ عَائِشَةَ زَوْجَ النَّبِيِّ صلى الله عليه وسلم مَا كَانَ أَكْثَرَ مَا يَدْعُو بِهِ رَسُولُ اللَّهِ صلى الله عليه وسلم قَبْلَ مَوْتِهِ قَالَتْ كَانَ أَكْثَرَ مَا كَانَ يَدْعُو بِهِ " اللَّهُمَّ إِنِّي أَعُوذُ بِكَ مِنْ شَرِّ مَا عَمِلْتُ وَمِنْ شَرِّ مَا لَمْ أَعْمَلْ " .
sunnah.com