رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 1756
The Book of the Prohibited actions
Undesirability of Glancing in one Direction of the other during Prayer
وَعَنْ أَنَسٍ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ لِي رَسُولُ اللَّهِ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ : إِيَّاكَ وَالِالْتِفَاتَ فِي الصَّلَاةِ، فَإِنَّ الِالْتِفَاتَ فِي الصَّلَاةِ هَلَكَةٌ، فَإِنْ كَانَ لابد، فَفِي التَّطَوُّع لَا فِي الفريضة .((رَوَاهُ التِّرْمِذِيُّ وَقَالَ حَدِيثٌ حَسَن صَحِيح)).
Anas (May Allah be pleased with him) said: The Messenger of Allah (ﷺ) said to me, "Beware of looking around in Salat (prayer), because random looks in Salat are a cause of destruction. If there should be no help from it, it is permissible in the voluntary and not in obligatory Salat." [At-Tirmidhi].
Riyad as-Salihin, 1756