The people asked: Messenger 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.
In-book : Book 43, Hadith 293
English translation : Book 42, Hadith 5047