There are 20 ayaat in this surah and it was revealed in Makkah. Some scholars say that it was revealed in Madinah. It is narrated from the Holy Prophet SallALLAHU Alayhe Wasallam that a person who recites this surah 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.
Imam Ja’far as-Sadiq AlayhisSalam said that a person who recites this surah properly will get a chance to meet the Holy Prophet Subhanahu Wata ‘Ala and if he prays for something from Allah Subhanahu Wata ‘Ala 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.

theislamonline.com

theislamonline.com

The reading of Quaranic-dua-2B-2  “Al-Mughni” (The Enricher) 1100 times and Surah Muzammil 7 is very effective in acquiring sufficiency of the heart.