Hadith
Abu Hurairah (May Allah be pleased with him) reported:
Messenger of Allah (ﷺ) said: "By Him in Whose Hand my soul is! You will not enter Jannah until you believe, and you shall not believe until you love one another. May I inform you of something, if you do, you love each other. Promote greeting amongst you (by saying As-salamu 'alaikum to one another)".
Authentic
Sahih Muslim