Al-Adab Al-Mufrad, Book 45, Hadith 1123 (English) ⓘ
Abu Mas'ud al-Jurayri related to him that a man asked al-Hasan about reading, "In the Name of Allah, the All-Merciful, Most Merciful." He said, "That should be put at the beginning of letters."
حَدَّثَنَا مُحَمَّدٌ الأَنْصَارِيُّ، قَالَ: حَدَّثَنَا أَبُو مَسْعُودٍ الْجُرَيْرِيُّ قَالَ: سَأَلَ رَجُلٌ الْحَسَنَ عَنْ قِرَاءَةِ بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ؟ قَالَ: تِلْكَ صُدُورُ الرَّسَائِلِ.
also referenced under: Hadith 1123 (Reference) & Book 45, Hadith 7 (In-Book)