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 (JA)
English reference (JA): Book 33, Hadith 214 (JA)
Arabic reference (JA): Book 34, Hadith 224 (JA)