Sahih Muslim Book - 6, Hadith - 1819

حَدَّثَنَا عَمْرٌو النَّاقِدُ وَزُهَيْرُ بْنُ حَرْبٍ قَالَ عَمْرٌو حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ عَنْ أَبِى الزِّنَادِ عَنِ الأَعْرَجِ عَنْ أَبِى هُرَيْرَةَ يَبْلُغُ بِهِ النَّبِىَّ -صلى الله عليه وسلم- « يَعْقِدُ الشَّيْطَانُ عَلَى قَافِيَةِ رَأْسِ أَحَدِكُمْ ثَلاَثَ عُقَدٍ إِذَا نَامَ بِكُلِّ عُقْدَةٍ يَضْرِبُ عَلَيْكَ لَيْلاً طَوِيلاً فَإِذَا اسْتَيْقَظَ فَذَكَرَ اللَّهَ انْحَلَّتْ عُقْدَةٌ وَإِذَا تَوَضَّأَ انْحَلَّتْ عُقْدَتَانِ فَإِذَا صَلَّى انْحَلَّتِ الْعُقَدُ فَأَصْبَحَ نَشِيطًا طَيِّبَ النَّفْسِ وَإِلاَّ أَصْبَحَ خَبِيثَ النَّفْسِ كَسْلاَنَ ».

It was narrated from Abu Hurairah that the Prophet (s.a.w) said: "The Shaitan ties three knots at the back of the head of any one of you when he goes to sleep, striking each knot and saying: 'You have a long night ahead, so sleep.' If he wakes up and remembers Allah, one knot is undone. If he performs Wudu', two knots are undone. If he prays, all the knots are undone, and he starts the day energetic and in a good mood. Otherwise, he starts his day in a bad mood and feeling lazy."'