Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
Bukhari :: Book 6 :: Volume 60 :: Hadith 237
Narrated Abu Huraira:
The Prophet said, "The recitation of Psalms (David's Quran) was made light and easy for David that he used to have his ridding animal be saddled while he would finish the recitation before the servant had saddled it."