بُلُوغُ الْمَرَامِ
Bulugh al-Maram 417
The Book of Prayer
وَعَنْ اِبْنِ عَبَّاسٍ رَضِيَ اَللَّهُ عَنْهُمَا قَالَ: { صَلَّيْتُ مَعَ رَسُولِ اَللَّهِ - صلى الله عليه وسلم -ذَاتَ لَيْلَةٍ, فَقُمْتُ عَنْ يَسَارِهِ, فَأَخَذَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -بِرَأْسِي مِنْ وَرَائِي, فَجَعَلَنِي عَنْ يَمِينِهِ } مُتَّفَقٌ عَلَيْه ِ [1] .
Narrated Ibn 'Abbas (RA): "I prayed (the night Tahajjud prayer) with Allah's Messenger (ﷺ) one night and I stood on his left side, whereupon he took me by the back of my head and made me go round to his right side. [Agreed upon].
Sunnah.com reference: Book 2, Hadith 322