The Messenger of Allah (ﷺ) said: Do you find me seeing towards the Qibla only? By Allah, your bowing and your prostrating are not hidden from my view. Verily I see them behind my back.
Sahih Muslim Book 4, Hadith 120
← Previous Hadith One day the Messenger of Allah (ﷺ) led the prayer. Then turning (towards his Companions) he said: O you man, why don't you say your prayer well? Does the observer of prayer not see how he is performing the prayer, for he performs it for himself? By Allah, I see behind me as I see in front of me.

Sahih Muslim Book 4, Hadith 119 Next Hadith → Perform bowing and prostration well. By Allah, I see you even if you are behind me, or he said: (I see you) behind my back when you bow or prostrate.

Sahih Muslim Book 4, Hadith 121