Surah 56. Al-Waqia, Ayah 79

I.e., which only the pure of heart can truly understand and derive benefit from. As for the preceding reference to "a well-guarded [i.e., incorruptible] divine writ" (kitab maknun), see {85:21-22} and the corresponding note [11].

 This verse refutes the pagan claim that the Quran was sent down by devils (see 26:210-212). Based on this verse, many jurists maintain that a Muslim should perform ablutions before reading the Quran.