Sunan an Nasai
The Book of The At-Tatbiq (Clasping One's Hands Together)
Hadith #65
12.65
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ عَمْرٍو، عَنْ طَاوُسٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ أُمِرَ النَّبِيُّ صلى الله عليه وسلم أَنْ يَسْجُدَ عَلَى سَبْعَةِ أَعْضَاءٍ وَلاَ يَكُفَّ شَعْرَهُ وَلاَ ثِيَابَهُ .
It was narrated that Ibn 'Abbas said:"The Prophet (ﷺ) was commanded to prostrate on seven parts of his body and not to tuck up his hair or his garment