The Angels are created from light.
Does the light sleep?
The Angels never ever sleep.
Do the Angels rest? They never ever rest; they work all the time.
[In the Bible, Jehovah, the Lord God rested in the 7th day of creation]
How come that the some creatures never ever rest and the Almighty Creator rests?
Well, then what the Angels do all the time?
The verse 21:20 says:
They glorify Allah night and day
They pray to Him at night and during the day; (they flag not)
They glorify His praises night and day, they never slacken.
They persist in their worship night and day, obeying Allah to the utmost
Thus, the verse paints a picture of creatures glorifying Allah and extolling His praises at all times.
However, the question is: do they get bored?
They do not get bored of worshipping Allah and of acknowledging His Lordship all the time.
They glorify Allah all the time, and they do not falter.
For Angels, glorifying Allah comes to them as naturally as breathing comes to us; it is something which we can never be distracted from.
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The verse 21:20 in four different translations
QARIB:
They (the Angels) never fail to exalt him either at night or in the day.
SHAKIR:
They (the Angels) glorify (him) by night and day; they are never languid
PICKTHAL:
They (the Angels) glorify (him) night and day; they flag not.
YUSUFALI:
They (the Angels) celebrate his praises night and day, nor do they ever flag or intermit.