Translation of the verse 6 from Surah Al-hijr : Number of verses 99 - - page 262 - Part 14.
And they say: "O you (Muhammad SAW) to whom the Dhikr (the Quran) has been sent down! Verily, you are a mad man.
And they say, "O you upon whom the message has been sent down, indeed you are mad.
(15:6) They say, "You, upon whom the Divine word *3 has been sent down, are surely insane.
*3) The word (Zikr) literally means "to cause to remember, "to caution" and "to give advice". But the Qur'an has used it as a technical term for "Admonition", which comes as a precept. Thus all the Books that had been sent down to the Messengers were Zikr, and the Qur'an is also Zikr.
Source : Al-hijr Verse 6: And they say, "O you upon whom the message has been sent down, indeed you are mad.