Sahih Al Bukhari 1: Chapter 3, Hadith 95

(95) Repeating one's talk thrice in order to make others understand

حَدَّثَنَا عَبْدَةُ بْنُ عَبْدِ اللَّهِ الصَّفَارُ، ‏‏‏‏‏‏حَدَّثَنَا عَبْدُ الصَّمَدِ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ الْمُثَنَّى، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنَا ثُمَامَةُ بْنُ عَبْدِ اللَّهِ، ‏‏‏‏‏‏عَنْ أَنَسٍ، ‏‏‏‏‏‏عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ، ‏‏‏‏‏‏"أَنَّهُ كَانَ إِذَا تَكَلَّمَ بِكَلِمَةٍ أَعَادَهَا ثَلَاثًا حَتَّى تُفْهَمَ عَنْهُ، ‏‏‏‏‏‏وَإِذَا أَتَى عَلَى قَوْمٍ فَسَلَّمَ عَلَيْهِمْ سَلَّمَ عَلَيْهِمْ ثَلَاثًا".

SAHIH HADITH:

Narrated Anas: Whenever the Prophet 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.

REFERENCE:

Sahih Al Bukhari 1: Chapter 3, Hadith 95