عن أنس رضي الله عنه
أن النبى صلى الله عليه وسلم كان إذا تكلم بكلمة أعادها ثلاثاً حتى تفهم عنه، وإذا أتى على قومٍ فسلم عليهم سلم عليهم ثلاثاً
Whenever the Prophet (sallallahu alayhi wa sallam) said something, he would repeat his words thrice so that the meanings would be understood fully; and whenever he came upon a group of people, he would greet them, and he would repeat salutation thrice.
Riyad as-Salihin 695, Book 2, The Book of Good Manners, Hadith 16. 1 min read