Anas reported that whenever the Prophet ﷺ spoke a word, he would repeat it three times so that it would be understood from him, and whenever he came upon a group of people and greeted them, he would greet them three times.
عن النبي ﷺ أنه كان إذا تكلم بكلمة أعادها ثلاثا حتى تفهم عنه، وإذا أتى على قوم فسلم عليهم سلم عليهم ثلاثا.
Bukhari related it in the Book of Knowledge (95), from Abda bin Abdullah, who said, Abdul-Samad told us, Abdullah bin Muthanna told us, Thumama bin Abdullah told us, from Anas, and he mentioned it.His statement, "He greeted them three times," means during the request for permission to enter.