Return every salam, equal or better

النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ خَلَقَ اللَّهُ آدَمَ عَلَى صُورَتِهِ، طُولُهُ سِتُّونَ ذِرَاعًا، فَلَمَّا خَلَقَهُ قَالَ اذْهَبْ فَسَلِّمْ عَلَى أُولَئِكَ النَّفَرِ مِنَ الْمَلاَئِكَةِ جُلُوسٌ، فَاسْتَمِعْ مَا يُحَيُّونَكَ، فَإِنَّهَا تَحِيَّتُكَ وَتَحِيَّةُ ذُرِّيَّتِكَ‏.‏ فَقَالَ السَّلاَمُ عَلَيْكُمْ‏.‏ فَقَالُوا السَّلاَمُ عَلَيْكَ وَرَحْمَةُ اللَّهِ‏.‏ فَزَادُوهُ وَرَحْمَةُ اللَّهِ، فَكُلُّ مَنْ يَدْخُلُ الْجَنَّةَ عَلَى صُورَةِ آدَمَ، فَلَمْ يَزَلِ الْخَلْقُ يَنْقُصُ بَعْدُ حَتَّى الآنَ ‏"‏‏.

“The Prophet ﷺ said, "Allah created Adam in His picture, sixty cubits (about 30 meters) in height. When He created him, He said (to him), "Go and greet that group of angels sitting there, and listen what they will say in reply to you, for that will be your greeting and the greeting of your offspring." Adam (went and) said, 'As-Salamu alaikum (Peace be upon you).' They replied, 'AsSalamu-'Alaika wa Rahmatullah (Peace and Allah's Mercy be on you) So they increased 'Wa Rahmatullah' The Prophet ﷺ added 'So whoever will enter Paradise, will be of the shape and picture of Adam Since then the creation of Adam's (offspring) (i.e. stature of human beings is being diminished continuously) to the present time”

حَقُّ الْمُسْلِمِ عَلَى الْمُسْلِمِ خَمْسٌ رَدُّ السَّلاَمِ، وَعِيَادَةُ الْمَرِيضِ، وَاتِّبَاعُ الْجَنَائِزِ، وَإِجَابَةُ الدَّعْوَةِ، وَتَشْمِيتُ الْعَاطِسِ ‏"‏‏.

“I heard Allah's Messenger ﷺ saying, "The rights of a Muslim on the Muslims are five: to respond to the salaam, visiting the sick, to follow the funeral processions, to accept an invitation, and to reply to those who sneeze. (see Hadith)”

أَمَرَنَا النَّبِيُّ صلى الله عليه وسلم بِسَبْعٍ، وَنَهَانَا عَنْ سَبْعٍ أَمَرَنَا بِاتِّبَاعِ الْجَنَائِزِ، وَعِيَادَةِ الْمَرِيضِ، وَإِجَابَةِ الدَّاعِي، وَنَصْرِ الْمَظْلُومِ، وَإِبْرَارِ الْقَسَمِ، وَرَدِّ السَّلاَمِ، وَتَشْمِيتِ الْعَاطِسِ‏.‏ وَنَهَانَا عَنْ آنِيَةِ الْفِضَّةِ، وَخَاتَمِ الذَّهَبِ، وَالْحَرِيرِ، وَالدِّيبَاجِ، وَالْقَسِّيِّ، وَالإِسْتَبْرَقِ‏.

“Allah's Messenger ﷺ ordered us to do seven things and forbade us to do other seven. He ordered us: to follow the funeral procession. to visit the sick, to accept invitations, to help the oppressed, to fulfill the oaths, to return the greeting and to reply to the sneezer: (saying, "May Allah be merciful on you," provided the sneezer says, "All the praises are for Allah,"). He forbade us to use silver utensils and dishes and to wear golden rings, silk (clothes), Dibaj (pure silk cloth), Qassi and Istabraq (two kinds of silk cloths)”