When you sleep, satan ties three knots on the back of your neck. And he says to each knot ” Let a long night stay with you”. When you wake up and cite the name of Allah one of the knots unties. When you make ablution another knot unties. And when you offer a prayer all of the knots unties. Thus, you wake you hale and hearty in the morning. Otherwise, you wake up asleep and downhearted.
[Bukhari ]