Sunan an-Nasai Book 50, Hadith 5465

أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، قَالَ حَدَّثَنَا عُثْمَانُ، - يَعْنِي الشَّحَّامَ - قَالَ حَدَّثَنَا مُسْلِمٌ، - يَعْنِي ابْنَ أَبِي بَكْرَةَ - أَنَّهُ كَانَ سَمِعَ وَالِدَهُ، يَقُولُ فِي دُبُرِ الصَّلاَةِ ‏ "‏ اللَّهُمَّ إِنِّي أَعُوذُ بِكَ مِنَ الْكُفْرِ وَالْفَقْرِ وَعَذَابِ الْقَبْرِ ‏"‏ ‏.‏ فَجَعَلْتُ أَدْعُو بِهِنَّ فَقَالَ يَا بُنَىَّ أَنَّى عُلِّمْتَ هَؤُلاَءِ الْكَلِمَاتِ قُلْتُ يَا أَبَتِ سَمِعْتُكَ تَدْعُو بِهِنَّ فِي دُبُرِ الصَّلاَةِ فَأَخَذْتُهُنَّ عَنْكَ ‏.‏ قَالَ فَالْزَمْهُنَّ يَا بُنَىَّ فَإِنَّ نَبِيَّ اللَّهِ صلى الله عليه وسلم كَانَ يَدْعُو بِهِنَّ فِي دُبُرِ الصَّلاَةِ ‏.‏

Muslim - meaning bin Abi Bakrah - narrated that:He heard his father say following the prayer: "Allahumma inni a'udhu bika minal-kufri wal-faqri, wa 'adhabil-qabri (O Allah, I seek refuge with You from Kufr, poverty and the torment of the grave.)" I started to recite them and he said: "O my son, where did you learn these words?" I said: "O my father, I heard you saying this supplication at the end of the prayer, and I learned them from you." He said: "Continue to recite them, O my son, for the Prophet of Allah [SAW] used to say this supplication at the end of the prayer