An-Nisaa 4:86

When you are given a greeting, respond with a better greeting or return the same[65]. Indeed, Allah is the Reckoner of all things.

[65] ‘Imrān ibn al-Husayn (رضي الله عنه) said: “A man came to the Prophet (ﷺ) and said: “Assalāmu ‘alaykum (Peace be upon you)”. He was replied to and sat down. The Prophet (ﷺ) said: “Ten (rewards)”. Then another one came and said: “Assalāmu ‘alaykum wa raḥmatu Allah (Peace be upon you and Allah’s Mercy)”. He was replied to and sat down. The Prophet (ﷺ) said: “Twenty”. Then another one came and said: “Assalāmu ‘alaykum wa raḥmatu Allah wa barakātuhu (Peace be upon you and Allah’s Mercy and His Blessings)”. He was replied to and sat down. The Prophet (ﷺ) said: “Thirty”. [Abū Dāwūd: 5195, At-Tirmidhī: 2689, Ahmad: 19948]

And when you are greeted with a greeting, greet [in return] with one better than it or [at least] return it [in a like manner]. Indeed Allāh is ever, over all things, an Accountant.

86. When you are greeted with a greeting, greet in return with what is better than it, or (at least) return it equally. Certainly, Allâh is Ever a Careful Account Taker of all things.[29]

[29] (V.4:86) How the Salâm (greeting) began.
Narrated Abu Hurairah رضي الله عنه : The Prophet صلى الله عليه وسلم said, "Allâh created Adam in His Image,* sixty cubits (about 30 metres) 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-Salâmu ‘Alaikum (peace be upon you)." They replied, "As-Salâmu ‘Alaikum wa Rahmatullah (Peace and Allâh’s Mercy be on you)." So they increased ‘wa Rahmatullah ’ " The Prophet صلى الله عليه وسلم 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 up to the present time." (Sahih Al-Bukhâri, Vol.8, Hadîth No.246).
*"His Image" means that Adam has been bestowed with life, knowledge, power of hearing, seeing, understanding, but the features of Adam are different from those of Allâh, only the names are the same, e.g., Allâh has life and knowledge and power of understanding, and Adam also has them, but there is no comparison between the Creator and the created thing. As Allâh says in the Qur’ân: "There is nothing like Him, and He is the All-Hearer, the All-Seer." (V.42:11), Allâh does not eat or sleep, while Adam used to eat and sleep [for details See Fath Al-Bâri, Vol.6, Page 108,9 and Vol.13, Page 238,9].

When ye are greeted with a greeting, greet ye with a better than it or return it. Lo! Allah taketh count of all things.