It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that whenever the Messenger of Allah (peace and blessings be upon him) said something, he would repeat it three times so that his (peace and blessings be upon him) words would be understood.
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 8064