Sahih Bukhari Volume 6, Book 61, Hadith Number 567.

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.