Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
tirmidhi:3640 – Muḥammad b. Yaḥyá > Abū Qutaybah Salm b. Qutaybah > ʿAbdullāh b. al-Muthanná > Thumāmah > Anas b. Mālik

that the Messenger of Allah ﷺ would repeat a statement three times so that it could be understood.  

الترمذي:٣٦٤٠ – حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى حَدَّثَنَا أَبُو قُتَيْبَةَ سَلْمُ بْنُ قُتَيْبَةَ عَنْ عَبْدِ اللَّهِ بْنِ الْمُثَنَّى عَنْ ثُمَامَةَ عَنْ أَنَسِ بْنِ مَالِكٍ قَالَ

كَانَ رَسُولُ اللَّهِ ﷺ يُعِيدُ الْكَلِمَةَ ثَلاَثًا لِتُعْقَلَ عَنْهُ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ غَرِيبٌ إِنَّمَا نَعْرِفُهُ مِنْ حَدِيثِ عَبْدِ اللَّهِ بْنِ الْمُثَنَّى

See similar narrations below:

Collected by Ḥākim
hakim:7716 – Abū Bakr Ismāʿīl b. Muḥammad b. Ismāʿīl Bi-al-Rray > Abū Ḥātim > Muḥammad b. ʿAbdullāh b. al-Muthanná al-Anṣārī from my father > Thumāmah > Anas b. Mālik

"When the Messenger of Allah ﷺ would give the Salam he would do so three times, and when he would say a statement, he would say it three times." (Using translation from Tirmidhī 2723)   

الحاكم:٧٧١٦ – حَدَّثَنَا أَبُو بَكْرٍ إِسْمَاعِيلُ بْنُ مُحَمَّدِ بْنِ إِسْمَاعِيلَ بِالرَّيِّ ثَنَا أَبُو حَاتِمٍ ثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ الْمُثَنَّى الْأَنْصَارِيُّ حَدَّثَنِي أَبِي ثَنَا ثُمَامَةُ عَنْ أَنَسِ بْنِ مَالِكٍ

«أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا تَكَلَّمَ بِكَلِمَةٍ أَعَادَهَا ثَلَاثًا لِتُعْقَلَ عَنْهُ»  

هَذَا حَدِيثٌ صَحِيحٌ عَلَى شَرْطِ الشَّيْخَيْنِ وَلَمْ يُخَرِّجَاهُ أخرجه البخاري سوى قوله لتعقل عنه