Sunan an-Nasa'i, Book 13, Hadith 23 (In-Book) ⓘ
It was narrated that Ibn 'Abbas said: "The Messenger of Allah used to turn to his right and left when praying, but he did not twist his neck to look behind him."
أَخْبَرَنَا أَبُو عَمَّارٍ الْحُسَيْنُ بْنُ حُرَيْثٍ، قَالَ حَدَّثَنَا الْفَضْلُ بْنُ مُوسَى، عَنْ عَبْدِ اللَّهِ بْنِ سَعِيدِ بْنِ أَبِي هِنْدٍ، عَنْ ثَوْرِ بْنِ زَيْدٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَلْتَفِتُ فِي صَلاَتِهِ يَمِينًا وَشِمَالاً وَلاَ يَلْوِي عُنُقَهُ خَلْفَ ظَهْرِهِ .
also referenced under: Hadith 1201 (Reference) & Volume 2, Book 13, Hadith 1202 (DarusSalam)