Sunan an-Nasa'i, Book 21, Hadith 171 (In-Book) ⓘ

It was narrated that Talhah bin 'Abdullah bin 'Awf said: "I offered the funeral prayer behind Ibn 'Abbas. He recited Fatihat Al-Kitab and a Surah, which he recited loudly, such that we could hear him. When he finished I took him by the hand and asked him. He said: '(It is) Sunnah and the truth."'

أَخْبَرَنَا الْهَيْثَمُ بْنُ أَيُّوبَ، قَالَ حَدَّثَنَا إِبْرَاهِيمُ، - وَهُوَ ابْنُ سَعْدٍ - قَالَ حَدَّثَنَا أَبِي، عَنْ طَلْحَةَ بْنِ عَبْدِ اللَّهِ بْنِ عَوْفٍ، قَالَ صَلَّيْتُ خَلْفَ ابْنِ عَبَّاسٍ عَلَى جَنَازَةٍ فَقَرَأَ بِفَاتِحَةِ الْكِتَابِ وَسُورَةٍ وَجَهَرَ حَتَّى أَسْمَعَنَا فَلَمَّا فَرَغَ أَخَذْتُ بِيَدِهِ فَسَأَلْتُهُ فَقَالَ سُنَّةٌ وَحَقٌّ ‏.‏