The Mercy of Allah
قَالَ عَلِيٌ )ع): إِذَا قَامَ الرَّجُلُ إِلـى الصَّلاَةِ أَقْبَلَ إِبْلِيسُ يَنْظُرُ إِلَيْهِ حَسَداً لِمَا يَرَى مِنْ رَحْمَةِ اللٌّهِ الَّتِي تَغْشَاهُ
Imam Ali (A.S) said: “When a person stands up for prayers, Iblis approaches him and looks at him with envy and jealousy, as he sees the Mercy of Allah encompassing the person.”
Biharul Anwar, Volume 82, Page 207
Other links:
The Face of Religion
The Conduct of the Prophets
Value of Prayers