عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ كَانَ إِذَا سَلَّمَ سَلَّمَ ثَلاَثًا، وَإِذَا تَكَلَّمَ بِكَلِمَةٍ أَعَادَهَا ثَلاَثًا.
Anas ibn Malik reported about the Prophet ﷺ that when he greeted, he greeted three times, and when he spoke a word, he repeated it three times.
also in Sahih al-Bukhari 95