Whenever the Prophet ﷺ asked permission to enter, he knocked the door thrice with greeting and whenever he spoke a sentence (said a thing) he used to repeat it thrice. (See Hadith No. 261, Vol. 8).  

عَنِ النَّبِيِّ ﷺ أَنَّهُ كَانَ إِذَا سَلَّمَ سَلَّمَ ثَلاَثًا وَإِذَا تَكَلَّمَ بِكَلِمَةٍ أَعَادَهَا ثَلاَثًا  

Whenever the Prophet ﷺ spoke a sentence (said a thing), he used to repeat it thrice so that the people could understand it properly from him and whenever he asked permission to enter, (he knocked the door) thrice with greeting.  

عَنِ النَّبِيِّ ﷺ أَنَّهُ كَانَ إِذَا تَكَلَّمَ بِكَلِمَةٍ أَعَادَهَا ثَلاَثًا حَتَّى تُفْهَمَ عَنْهُ وَإِذَا أَتَى عَلَى قَوْمٍ فَسَلَّمَ عَلَيْهِمْ سَلَّمَ عَلَيْهِمْ ثَلاَثًا  

Whenever Messenger of Allah ﷺ greeted somebody, he used to greet him three times, and if he spoke a sentence, he used to repeat it thrice.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا سَلَّمَ سَلَّمَ ثَلاَثًا وَإِذَا تَكَلَّمَ بِكَلِمَةٍ أَعَادَهَا ثَلاَثًا  

The Messenger of Allah ﷺ spoke in a distinct manner so that anyone who listened to him could understand it.  

كَانَ كَلاَمُ رَسُولِ اللَّهِ ﷺ كَلاَمًا فَصْلاً يَفْهَمُهُ كُلُّ مَنْ سَمِعَهُ