Abu Dawud Book 36, Hadith Number 5047.

Chapter : Not known.

Narated By Abdullah ibn Amr : The Prophet (PBUH) said: There are two qualities or characteristics which will not be returned by any Muslim without his entering Paradise. While they are easy, those who act upon them are few. One should say: “Glory be to Allah” ten times after every prayer, “Praise be to Allah” ten times and “Allah is Most Great” ten times. That is a hundred and fifty on the tongue, but one thousand and five hundred on the scale. When he goes to bed, he should say: “Allah is Most Great” thirty-four times, “Praise be to Allah” thirty-three times, and Glory be to Allah thirty-three times, for that is a hundred on the tongue and a thousand on the scale. (He said:) I saw the Apostle of Allah (PBUH) counting them on his hand.

The people asked: Apostle of Allah! How is it that while they are easy, those who act upon them are few?

He replied: The Devil comes to one of you when he goes to bed and he makes him sleep, before he utters them, and he comes to him while he is engaged in prayer and calls a need to his mind before he utters them.