It was narrated from 'Abdullah bin 'Abbas that:He saw 'Abdullah bin Al-Harith praying with his hair bound behind him. He stopped and started to undo it. When he finished he turned to Ibn 'Abbas and said: "What were you doing to my head?" He said: "I heard the Messenger of Allah (ﷺ) say: 'The likeness of this is that of one who prays with his hands tie behind his neck.'"
أَخْبَرَنَا عَمْرُو بْنُ سَوَّادِ بْنِ الأَسْوَدِ بْنِ عَمْرٍو السَّرْحِيُّ، - مِنْ وَلَدِ عَبْدِ اللَّهِ بْنِ سَعْدِ بْنِ أَبِي سَرْحٍ - قَالَ أَنْبَأَنَا ابْنُ وَهْبٍ، قَالَ أَنْبَأَنَا عَمْرُو بْنُ الْحَارِثِ، أَنَّ بُكَيْرًا، حَدَّثَهُ أَنَّ كُرَيْبًا مَوْلَى ابْنِ عَبَّاسٍ حَدَّثَهُ عَنْ عَبْدِ اللَّهِ بْنِ عَبَّاسٍ، أَنَّهُ رَأَى عَبْدَ اللَّهِ بْنَ الْحَارِثِ يُصَلِّي وَرَأْسُهُ مَعْقُوصٌ مِنْ وَرَائِهِ فَقَامَ فَجَعَلَ يَحُلُّهُ فَلَمَّا انْصَرَفَ أَقْبَلَ إِلَى ابْنِ عَبَّاسٍ فَقَالَ مَا لَكَ وَرَأْسِي قَالَ إِنِّي سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " إِنَّمَا مَثَلُ هَذَا مَثَلُ الَّذِي يُصَلِّي وَهُوَ مَكْتُوفٌ " .
Nesai
The Book of The At-Tatbiq (Clasping One's Hands Together) • Hadith 1114