The Prophet ﷺ said, "Recitation was made easy for Dawud. He would order his mount to be saddled, and he would finish reciting it before the saddling was complete," meaning the Quran.
عن النبي ﷺ قال: خفف على داود القراءة، فكان يأمر بدابته لتسرج، فكان يقرأ قبل أن يفرغ. يعني القرآن.
Bukhari related it in the Tafsir (4713), from Ishaq bin Nasr, who said, Abdul-Razzaq narrated to us, from Mamar, from Hammam bin Munabbih, from Abu Hurairah, and he mentioned it.His saying, "He used to recite before he finished," means the Quran. What is meant by it is the Zabur that Allah had given him, which is what is called in the Old Testament "the Psalms," numbering 150. What is meant by "Quran" here is not the Quran known to this ummah.