La tadkhulunal-jannata hatta tu'minu wala tu'minu hatta tahabbu. awala adullukum 'ala sha'in idha fa'altumuhu tahababtum afshus-salama baynakum
You will not enter Paradise until you believe, and you will not believe until you love one another. Shall I not guide you to something which, if you do it, you will love one another? Spread the greeting of peace among you.
ʿAmmār (may Allah be pleased with him) is reported to have said that whoever brings together three things has brought together faith: fairness from oneself, offering the greeting of peace to everyone, and spending even when in want.
Source as cited by the compiler al-Bukhārī (Fatḥ al-Bārī 1/82), as a saying of ʿAmmār, muʿallaq