Sunan Ibn Majah 844
It was
narrated that Samurah bin Jundab said:
“There are two pauses
which I memorized from the Messenger of Allah (ﷺ), but `Imran bin
Husain denied that. We wrote to Ubayy bin Ka`b in Al-Madinah, and
he
wrote that Samurah had indeed memorized them.”

(One of the narrators) Sa`eed said: "We said to Qatadah: 'What are these two pauses?' He said: 'When he started his prayer, and when he finished reciting.'

Then later he said: 'And when he recited: 'Not (the way) of those who earned your anger, nor of those who went astray.' They used to like (for the Imam) when he had finished reciting to remain silent until he had caught his breath.'"
حَدَّثَنَا جَمِيلُ بْنُ الْحَسَنِ بْنِ جَمِيلٍ الْعَتَكِيُّ، حَدَّثَنَا عَبْدُ الأَعْلَى، حَدَّثَنَا سَعِيدٌ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، عَنْ سَمُرَةَ بْنِ جُنْدُبٍ، قَالَ سَكْتَتَانِ حَفِظْتُهُمَا عَنْ رَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ ‏.‏ فَأَنْكَرَ ذَلِكَ عِمْرَانُ بْنُ الْحُصَيْنِ فَكَتَبْنَا إِلَى أُبَىِّ بْنِ كَعْبٍ بِالْمَدِينَةِ فَكَتَبَ أَنَّ سَمُرَةَ قَدْ حَفِظَ ‏.‏ قَالَ سَعِيدٌ فَقُلْنَا لِقَتَادَةَ مَا هَاتَانِ السَّكْتَتَانِ قَالَ إِذَا دَخَلَ فِي صَلاَتِهِ وَإِذَا فَرَغَ مِنَ الْقِرَاءَةِ ‏.‏ ثُمَّ قَالَ بَعْدُ وَإِذَا قَرَأَ ‏{غَيْرِ الْمَغْضُوبِ عَلَيْهِمْ وَلاَ الضَّالِّينَ}‏ ‏.‏ قَالَ وَكَانَ يُعْجِبُهُمْ إِذَا فَرَغَ مِنَ الْقِرَاءَةِ أَنْ يَسْكُتَ حَتَّى يَتَرَادَّ إِلَيْهِ نَفَسُهُ ‏.‏