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]. (AR)
App reference (AR): Book 2, Hadith 16 (AR)
Arabic/English book reference (AR): Book 2, Hadith 696 (AR)