Aisha reported: I asked the Messenger of Allah, peace and blessings be upon him, about fidgeting in the prayer. The Prophet said, “It is theft by which Satan steals from the prayer of a servant.”
Source: Ṣaḥīḥ al-Bukhārī 718
Grade: Sahih (authentic) according to Al-Bukhari
عَنْ عَائِشَةَ قَالَتْ سَأَلْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَنْ الِالْتِفَاتِ فِي الصَّلَاةِ فَقَالَ هُوَ اخْتِلَاسٌ يَخْتَلِسُهُ الشَّيْطَانُ مِنْ صَلَاةِ الْعَبْدِ
718 صحيح البخاري أبواب صفة الصلاة باب الالتفات في الصلاة