It was the practice of the Prophet (peace and blessings be upon him):
"His (peace and blessings be upon him) speech was clear and distinct, understood by everyone who heard it."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4826
Hadith Gradingالألبانی:حسن
Hadith Takhrij[د] عن عائشة. الصحيحة ٢٠٩٧: حم، ابن سعد.