Hadith: A man came to the Prophet (may Allah's peace and blessings be upon him) and said: As-salāmu ‘alaykum (peace be upon you). He responded to him and then sat down. The Prophet (may Allah's peace and blessings be upon him) said: "Ten

عَنْ عِمْرَانَ بْنِ حُصَيْنٍ رَضِيَ اللَّهُ عَنْهُ قَالَ:
جَاءَ رَجُلٌ إِلَى النَّبِيِّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ فَقَالَ: السَّلَامُ عَلَيْكُمْ، فَرَدَّ عَلَيْهِ ثُمَّ جَلَسَ، فَقَالَ النَّبِيُّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: «عَشْرٌ» ثُمَّ جَاءَ آخَرُ فَقَالَ: السَّلَامُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ، فَرَدَّ عَلَيْهِ فَجَلَسَ، فَقَالَ: «عِشْرُونَ» ثُمَّ جَاءَ آخَرُ فَقَالَ: السَّلَامُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ وَبَرَكَاتُهُ، فَرَدَّ عَلَيْهِ فَجَلَسَ، فَقَالَ: «ثَلَاثُونَ».
[حسن] - [رواه أبو داود والترمذي وأحمد والدارمي] - [سنن أبي داود: 5195]

‘Imrān ibn Husayn (may Allah be pleased with him) reported:
A man came to the Prophet (may Allah's peace and blessings be upon him) and said: As-salāmu ‘alaykum (peace be upon you). He responded to him and then sat down. The Prophet (may Allah's peace and blessings be upon him) said: "Ten." Then another came and said: As-salāmu ‘alaykum wa rahmatullāh (may the peace and mercy of Allah be upon you). He responded to him and so he sat down. He said: "Twenty." Then another came and said: As-salāmu ‘alaykum wa rahmatullāh wa barakātuh (may the peace, mercy, and blessings of Allah be upon you). He responded to him and so he sat down. He said: "Thirty."
[Good hadith] - - [Sunan Abu Daoud - 5195]

Explanation

A man came to the Prophet (may Allah's peace and blessings be upon him) and said: (Peace be upon you). The Prophet (may Allah's peace and blessings be upon him) responded to him and then he sat down. The Prophet (may Allah's peace and blessings be upon him) said: Ten good deeds have been written for him. Then another came and said: (May the peace and mercy of Allah be upon you). The Prophet (may Allah's peace and blessings be upon him) responded to him, and so he sat down. The Prophet (may Allah's peace and blessings be upon him) said: Twenty good deeds have been written for him. Then another came and said: (May the peace, mercy, and blessings of Allah be upon you). The Prophet (may Allah's peace and blessings be upon him) responded to him, and so he sat down. The Prophet (may Allah's peace and blessings be upon him) said: Thirty good deeds have been written for him, i.e., ten good deeds are counted for each word.

Benefits from the Hadith

1. The comer should begin greeting those who are already sitting.
2. The reward increases with the increase of the words of the greeting of peace.
3. The most perfect form of greeting someone with peace is: (May the peace, mercy, and blessings of Allah be upon you), and the best response is: (And upon you be the peace, mercy, and blessings of Allah).
4. The greeting of peace and the response have various levels and the reward varies as well.
5. Teaching people what is good and drawing their attention to seek what is better.
6. Ibn Hajar said: If the one initiating the greeting adds (and mercy of Allah), it is recommended to respond with (and His blessings). However, if the initiator adds (and His blessings), is further addition permissible in the reply? Similarly, if the initiator goes beyond (and His blessings), is this permissible for him? Mālik narrated in Al-Muwatta’ on the authority of Ibn ‘Abbās (may Allah be pleased with him and his father) that he said: The greeting of peace ends with the blessing.