Anas (May Allah be pleased with him) reported:
Whenever the Prophet (ﷺ) 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.
[Al-Bukhari and Muslim].
App reference: Book 2, Hadith 16
Arabic/English book reference: Book 2, Hadith 696