There are 20 ayaat in surah muzzammil and it was revealed in Makkah. Some scholars say that surah muzzammil was revealed in Madinah. It is narrated from the Holy Prophet (s.a.w.) that a person who recites surah muzzammil will never face bad times. The person who recites it in the Isha or Tahajjud prayers always remains pure of heart and even dies while he is in a pure state.
Who recites surah muzzammil properly will get a chance to meet the Holy Prophet (s.a.w.) and if he prays for something from Allah (S.W.T.) he will get it. Reciting surah al-Muzammil a hundred times on Thursday night leads to the forgiving of a hundred major sins and procures a hundred rewards. Recitation of this surah protects one from insanity and from being a slave to people.