وعن أنس رضي الله عنه
أن النبي صلى الله عليه وسلم، كان إذا تكلم بكلمة أعادها ثلاثًا حتى تفهم عنه، وإذا أتى على قوم فسلم عليهم سلم عليهم ثلاثًا
Anas (radiyallahu anhu) reported the Prophet (sallallahu alayhi wa sallam) used to repeat his words thrice so that the meaning thereof would be fully understood, and whenever he came upon a gathering of people, he would greet them. He would repeat Salam thrice.
Riyad as-Salihin 852, Book 6, The Book of Greetings, Hadith 9. 1 min read