"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."  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يَلْحَظُ فِي الصَّلاَةِ يَمِينًا وَشِمَالاً وَلاَ يَلْوِي عُنُقَهُ خَلْفَ ظَهْرِهِ  

"The Prophet would glance during Salat" and he mentioned a similar narration.  

أَنَّ النَّبِيَّ ﷺ كَانَ يَلْحَظُ فِي الصَّلاَةِ فَذَكَرَ نَحْوَهُ قَالَ وَفِي الْبَابِ عَنْ أَنَسٍ وَعَائِشَةَ  

"The Messenger of Allah said to me: 'O my son! Beware of looking around during the Salat, for indeed looking around during Salat is destruction. If you must do so, then in the voluntary (prayers), not in the obligatory (prayers).'" (Da'if)  

لِي رَسُولُ اللَّهِ ﷺ يَا بُنَىَّ إِيَّاكَ وَالاِلْتِفَاتَ فِي الصَّلاَةِ فَإِنَّ الاِلْتِفَاتَ فِي الصَّلاَةِ هَلَكَةٌ فَإِنْ كَانَ لاَ بُدَّ فَفِي التَّطَوُّعِ لاَ فِي الْفَرِيضَةِ  

"I asked the Messenger of Allah about looking around during the Salat. He said: 'It is a portion which the Shaitan snatches during a man's prayer.'"  

سَأَلْتُ رَسُولَ اللَّهِ ﷺ عَنْ الاِلْتِفَاتِ فِي الصَّلاَةِ قَالَ هُوَ اخْتِلاَسٌ يَخْتَلِسُهُ الشَّيْطَانُ مِنْ صَلاَةِ الرَّجُلِ