Hadith: A man asked the Messenger of Allah (may Allah's peace and blessings be upon him): Which deed in Islam is the best? He said: Feeding people and extending the greeting of peace to those you know and those you do not know.

عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو رَضِيَ اللَّهُ عَنْهُمَا:

أَنَّ رَجُلًا سَأَلَ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: أَيُّ الإِسْلاَمِ خَيْرٌ؟ قَالَ: «تُطْعِمُ الطَّعَامَ، وَتَقْرَأُ السَّلاَمَ عَلَى مَنْ عَرَفْتَ وَمَنْ لَمْ تَعْرِفْ».
[صحيح] - [متفق عليه]

‘Abdullāh ibn ‘Amr ibn al-‘Ās (may Allah be pleased with him) reported: A man asked the Messenger of Allah (may Allah's peace and blessings be upon him): "Which deed in Islam is the best?" He said: "Feeding people and extending the greeting of peace to those you know and those you do not know."
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

The Companions of the Prophet (may Allah's peace and blessings be upon him) asked him which act is the best in Islam, meaning: What Islamic manners or traits are more virtuous in terms of reward or more beneficial? The Prophet (may Allah's peace and blessings be upon him) replied that it is to give food to people and to extend the greeting of peace to people whether you know them or not.