Sahih Bukhari Volume 6, Book 66, Hadith 5049

حَدَّثَنَا آدَمُ بْنُ أَبِي إِيَاسٍ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا أَبُو إِيَاسٍ، قَالَ سَمِعْتُ عَبْدَ اللَّهِ بْنَ مُغَفَّلٍ، قَالَ رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم يَقْرَأُ وَهْوَ عَلَى نَاقَتِهِ ـ أَوْ جَمَلِهِ ـ وَهْىَ تَسِيرُ بِهِ وَهْوَ يَقْرَأُ سُورَةَ الْفَتْحِ أَوْ مِنْ سُورَةِ الْفَتْحِ قِرَاءَةً لَيِّنَةً يَقْرَأُ وَهْوَ يُرَجِّعُ‏

Narrated By 'Abdullah bin Mughaffal : I saw the Prophet reciting (Qur'an) while he was riding on his she camel or camel which was moving, carrying him. He was reciting Surat Fath or part of Surat Fath very softly and in an Attractive vibrating tone.