Arabic text
عَنْ أَبِي هُرَيْرَةَ رضي الله عنه قَالَ: قَالَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: «لَا تَدْخُلُونَ الْجَنَّةَ حَتَّى تُؤْمِنُوا، وَلَا تُؤْمِنُوا حَتَّى تَحَابُّوا، أَوَلَا أَدُلُّكُمْ عَلَى شَيْءٍ إِذَا فَعَلْتُمُوهُ تَحَابَبْتُمْ؟ أَفْشُوا السَّلَامَ بَيْنَكُمْ».
Translation
Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "You will not enter Paradise until you believe and you will not believe until you love one another. Shall I guide you to something which, if you do, you will love one another? Spread the greeting of peace among yourselves."
Explanation
The Prophet (may Allah's peace and blessings be upon him) clarified that none will enter Paradise except the believers, and faith will not be perfect and the Muslim society will not be in good condition unless they love one another. Then, the Prophet (may Allah's peace and blessings be upon him) guided us to the best means of spreading love, namely spreading the greeting of peace among Muslims, as Allah has made peace a greeting for His slaves.
Source: HadeethEnc.com