Hadith: The speech of the Messenger of Allah (may Allah's peace and blessings be upon him) was clearly articulated that anyone who listened to him could understand it

عن عائشة رضي الله عنها قالت: كَانَ كَلاَمُ رَسُولِ الله -صلَّى الله عليه وسلَّم- كَلاَمًا فَصلاً يَفْهَمُهُ كُلُّ مَنْ يَسْمَعُهُ.
[حسن] - [رواه أبو داود واللفظ له، والتُرمذي والنسائي وأحمد]

‘Ā'ishah (may Allah be pleased with her) reported: The speech of the Messenger of Allah (may Allah's peace and blessings be upon him) was clearly articulated that anyone who listened to him could understand it.
[Good hadith] - [Narrated by At-Termedhy - An-Nasaa’i - Narrated by Abu Daoud - Narrated by Ahmad]

Explanation

‘Ā'ishah (may Allah be pleased with her) said that the speech of the Prophet (may Allah's peace and blessings be upon him) was so clearly articulated. It was clear to all those who heard it, and was neither complicated nor wordy; even if one wished to count his words, it would be easy because the Prophet (may Allah's peace and blessings be upon him) used to speak at a very moderate pace. Moreover, the Prophet (may Allah's peace and blessings be upon him) was gifted with the ability to speak brief yet comprehensive words. He used to speak very concisely. One should not mumble when speaking lest it should be vague for the listener. Obviously, the purpose of speaking is to help the addressee understand what one says; the more understandable one's speech is, the better it is. When one uses this method, i.e. clearly articulating his speech, and repeats it three times for whoever cannot understand, he should realize that he is imitating the Prophet (may Allah's peace and blessings be upon him) to be rewarded and help his brother understand what he says. The same applies to all acts of the Sunnah. One should always keep in mind that he is following the Prophet (may Allah's peace and blessings be upon him) to be counted among those who adhere to the Sunnah and, thus, be rewarded.