The Prophet ﷺ said, "Perform the bowing and prostration properly, for by Allah, I see you from behind me," and sometimes he said, "from behind my back, when you bow and prostrate."
عن النبي ﷺ قال: أقيموا الركوع والسجود، فوالله إني لأراكم من بعدي- وربما قال: من بعد ظهري- إذا ركعتم وسجدتم.
Bukhari reported it in the Book of Adhan (742), and Muslim reported it in the Book of Prayer (110:425), both from Muhammad bin Bashshar, who said, Ghundar Muhammad bin Jafar narrated to us, who said, Shubah narrated to us, who said, I heard Qatada narrate from Anas bin Malik, and he related it.Nawawi said in his commentary on Sahih Muslim, "The scholars said, its meaning is that Allah created for him a perception in the back of his head with which he could see what was behind him. Custom has been broken for him ﷺ in more than this, and neither reason nor the Sacred Law prevents this. Rather, the Sacred Law came with its apparent meaning, so it must be affirmed as it is."The qadi said, "Ahmad bin Hanbal, may Allah have mercy on him, and the majority of scholars said, this vision is a real vision with the eye." End of quote.