Abdullah ibn Amr reported: A man asked the Messenger of Allah, peace and blessings be upon him, “Which Islam is best?” The Prophet said, “To feed the hungry and to greet with peace those you know and those you do not know.”

Source: Sahih Bukhari 28

Grade: Sahih (authentic) according to Al-Bukhari

عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو أَنَّ رَجُلاً سَأَلَ رَسُولَ اللَّهِ صلى الله عليه وسلم أَىُّ الإِسْلاَمِ خَيْرٌ قَالَ تُطْعِمُ الطَّعَامَ وَتَقْرَأُ السَّلاَمَ عَلَى مَنْ عَرَفْتَ وَمَنْ لَمْ تَعْرِفْ

28 صحيح البخاري كِتَاب الْإِيمَانِ بَاب إِفْشَاءُ السَّلَامِ مِنْ الْإِسْلَامِ