Surah 21. Al-Anbiya, Ayah 42

The reference to God, in this context, as "the Most Gracious" (ar-rahman) is meant to bring out the fact that He - and He alone - is the protector of all creation.

'Allah is most Gracious: if, in spite of His great mercy, you are so rebellious and depraved as to incur His Wrath, who is there who can save you? His Wrath can descend on you at any time, by night or by day.'