Shama-il Tirmidhi Chapter 33, Hadith Number 2 (214).

Anas ibn Maalik radiyallahu anhu says, Rasoolullah sallallahu alaihe wasallam (sometimes) repeated a word (as was necessary) thrice, so that his listeners understood well what he was saying.

If what he was explaining was difficult or it was something that had to be given a thought, or if there were many people, he faced all three sides and repeated it to every side, so that those present understood well what he was said. Repeating a thing thrice was maximum. If saying a thing twice only sufficed, he only said it twice.