مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 996
Prayer
What may not be done during Prayer and what is permitted - Section 2
وَعَنْ أَنَسٍ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «يَا أَنَسُ اجْعَلْ بَصَرَكَ حَيْثُ تَسْجُدُ» . رَوَاهُ الْبَيْهَقِيُّ فِي سُنَنِهِ الْكَبِيرِ مِنْ طَرِيق الْحسن عَن أنس يرفعهُ
Anas told that the Prophet (ﷺ) said, “Keep looking in the direction towards which you prostrate yourself, Anas.” Baihaqi transmitted it in [Kitab] as-sunan al-kabir through al-Hasan from Anas, tracing it back to the Prophet.
Mishkat al-Masabih, 996ضَعِيف (الألباني)