A man asked the Messenger of Allah (May peace be upon him): When aspect of Islam is best? He replied: that you should provide food and greet both those you know and those you do not know.
Sunan Abi Dawud Book 43, Hadith 422
← Previous Hadith By him in whose hand my soul is, you will not enter Paradise until you believe, and you will not believe until you love one another: should I not guide you to something doing which you will love one another: spread out salutation among you.

Sunan Abi Dawud Book 43, Hadith 421 Next Hadith → 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.

Sunan Abi Dawud Book 43, Hadith 423