This is Chapter 59 of Holy Quran.
This Surah is ‘madani’ and it has 24 ayaat. It is narrated that whoever recites this Surah will be sent salutations from Jannah, Jahannam, the angels, the Heavens, the Earth, the trees, the birds, the sun and the moon and these will pray for the forgiveness of his sins. When he dies, he will die a martyr. If a person recites both Surah ar-Rahman and Surah al-Hashr then one angel will be assigned to protect him at all times.
If a four-rak’ah prayer is recited where after Surah al-Hamd Surah al-Hashr is recited, then whatever important work one goes to do will be successful (with the condition that it is not a sin). Drinking water in which this Surah has been dissolved is good for memory and concentration. If this Surah is recited for forty consecutive days without missing a day, it will make even the hardest task become an easy one.