Sahih Muslim Book 4, Hadith 119
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.
This hadith is transmitted by Muhammad b. Rafi', Abu'I-Razzaq. Ma'mar, Hammam on the authority of Abu Huraira with the addition of (the word)" prayer".
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.