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.  

قَالَ رَسُولُ اللَّهِ ﷺ وَالَّذِي نَفْسِي بِيَدِهِ لاَ تَدْخُلُوا الْجَنَّةَ حَتَّى تُؤْمِنُوا وَلاَ تُؤْمِنُوا حَتَّى تَحَابُّوا أَفَلاَ أَدُلُّكُمْ عَلَى أَمْرٍ إِذَا فَعَلْتُمُوهُ تَحَابَبْتُمْ أَفْشُوا السَّلاَمَ بَيْنَكُمْ  

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.  

أَنَّ رَجُلاً سَأَلَ رَسُولَ اللَّهِ ﷺ أَىُّ الإِسْلاَمِ خَيْرٌ قَالَ تُطْعِمُ الطَّعَامَ وَتَقْرَأُ السَّلاَمَ عَلَى مَنْ عَرَفْتَ وَمَنْ لَمْ تَعْرِفْ