A man came to the Prophet ﷺ and said: Peace be upon you! He responded to his salutation. He then sat down. The Prophet ﷺ said: Ten. Another man came and said: Peace and Allah's mercy be upon you! He responded to his salutation when he sat down. He said: Twenty. Another man came and said: Peace and Allah's mercy and blessings be upon you! He responded to him and said when he sat down: and blessings be upon you! He responded to him and said when he sat down: Thirty.  

جَاءَ رَجُلٌ إِلَى النَّبِيِّ ﷺ فَقَالَ السَّلاَمُ عَلَيْكُمْ فَرَدَّ عَلَيْهِ السَّلاَمَ ثُمَّ جَلَسَ فَقَالَ النَّبِيُّ ﷺ عَشْرٌ ثُمَّ جَاءَ آخَرُ فَقَالَ السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ فَرَدَّ عَلَيْهِ فَجَلَسَ فَقَالَ عِشْرُونَ ثُمَّ جَاءَ آخَرُ فَقَالَ السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ وَبَرَكَاتُهُ فَرَدَّ عَلَيْهِ فَجَلَسَ فَقَالَ ثَلاَثُونَ  

that the Messenger of Allah ﷺ said: "O 'Aishah! Here is Jibril and he is giving Salam to you." She said: "I said: 'And upon him be peace and the mercy of Allah, and His blessings. You see that which we do not.'"  

قَالَ رَسُولُ اللَّهِ ﷺ يَا عَائِشَةُ هَذَا جِبْرِيلُ وَهُوَ يَقْرَأُ عَلَيْكِ السَّلاَمَ قَالَتْ قُلْتُ وَعَلَيْهِ السَّلاَمُ وَرَحْمَةُ اللَّهِ وَبَرَكَاتُهُ تَرَى مَا لاَ نَرَى  

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  

that the Messenger of Allah ﷺ passed through the Masjid one day, and a group of women were sitting, so he motioned his hand with the Salam - 'Abdul-Hamid (one of the narrators) gestured with his hand.  

أَنَّ رَسُولَ اللَّهِ ﷺ مَرَّ فِي الْمَسْجِدِ يَوْمًا وَعُصْبَةٌ مِنَ النِّسَاءِ قُعُودٌ فَأَلْوَى بِيَدِهِ بِالتَّسْلِيمِ وَأَشَارَ عَبْدُ الْحَمِيدِ بِيَدِهِ  

I came to the Prophet ﷺ and said: Upon you be peace, Messenger of Allah! He said: Do not say: Upon you be peace, for "Upon you be peace" is the salutation to the dead.  

أَتَيْتُ النَّبِيَّ ﷺ فَقُلْتُ عَلَيْكَ السَّلاَمُ يَا رَسُولَ اللَّهِ قَالَ لاَ تَقُلْ عَلَيْكَ السَّلاَمُ فَإِنَّ عَلَيْكَ السَّلاَمُ تَحِيَّةُ الْمَوْتَى