«كان إذا تكلم بكلمة أعادها ثلاثا حتى تفهم عنه وإذا أتى على قوم فسلم عليهم سلم عليهم ثلاثا»
It was the practice of the Prophet (peace and blessings be upon him):
"When he (peace and blessings be upon him) said something, he would repeat it three times so that it would be understood, and when he (peace and blessings be upon him) came to a people and greeted them with salam, he would greet them three times."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4694