عن أبي هريرة رضي الله عنه في حديث المسيء صلاته
أنه جاء فصلى، ثم جاء النبي صلى الله عليه وسلم، فسلم عليه، فرد عليه السلام، فقال: «ارجع فصلِ، فإنك لم تصلِ«فرجع فصلى، ثم جاء فسلم على النبي صلى الله عليه وسلم، حتى فعل ذلك ثلاث مرات»
He came to the Prophet (sallallahu alayhi wa sallam) and greeted him. The Prophet (sallallahu alayhi wa sallam) responded to the greeting and said, “Go back and repeat your Salat because you have not performed the Salat (properly).” He again performed Salat as he had prayed before and came to the Prophet (sallallahu alayhi wa sallam) and greeted him.
The Prophet (sallallahu alayhi wa sallam) responded to the greetings (and repeated his words to him). This act of repeating (the Salat and the Salam) was done thrice.
Riyad as-Salihin 859, Book 6, The Book of Greetings, Hadith 16. 1 min read