What may not be done during Prayer and what is permitted - Section 1 Mishkat al-Masabih 982
Arabic hadith text
وَعَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ: سَأَلَتْ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَنِ الِالْتِفَاتِ فِي الصَّلَاةِ فَقَالَ: «هُوَ اختلاس يختلسه الشَّيْطَان من صَلَاة العَبْد»
Translation
‘A’isha said
I asked God’s Messenger about looking to the side during prayer and he said, “It is something which the devil snatches from a servant’s prayer.” (Bukhari and Muslim.)