Jami` at-Tirmidhi 587
جامع الترمذي#587Sahihحَدَّثَنَا مَحْمُودُ بْنُ غَيْلاَنَ، وَغَيْرُ، وَاحِدٍ، قَالُوا حَدَّثَنَا الْفَضْلُ بْنُ مُوسَى، عَنْ عَبْدِ اللَّهِ بْنِ سَعِيدِ بْنِ أَبِي هِنْدٍ، عَنْ ثَوْرِ بْنِ زَيْدٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَلْحَظُ فِي الصَّلاَةِ يَمِينًا وَشِمَالاً وَلاَ يَلْوِي عُنُقَهُ خَلْفَ ظَهْرِهِ . قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ غَرِيبٌ . وَقَدْ خَالَفَ وَكِيعٌ الْفَضْلَ بْنَ مُوسَى فِي رِوَايَتِهِ .
Ibn Abbas narrated:"The Messenger of Allah would glance toward the right and the left during Salat but he would not turn his neck to look behind him
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 6:44