Talha b. ‘Abdallah b. ‘Auf said he prayed behind Ibn ‘Abbas at a funeral and he recited <i>Fatihat al-Kltab</i> (Qur'an, sura i). He then said that it was to let them know it was a <i>sunna</i>. Bukhari transmitted it.

وَعَنْ طَلْحَةَ بْنِ عَبْدِ اللَّهِ بْنِ عَوْفٍ قَالَ: صَلَّيْتُ خَلْفَ ابْنِ عَبَّاسٍ عَلَى جَنَازَةٍ فَقَرَأَ فَاتِحَةَ الْكِتَابِ فَقَالَ: لِتَعْلَمُوا أَنَّهَا سُنَّةٌ. رَوَاهُ البُخَارِيّ