Az-Zubair bin Al-'Awwam narrated that the Prophet (s.a.w) said:
"The disease of the nations before you is creeping towards you: Envy and hatred, it is the Haliqah. I do not speak of what cuts the hair, but what severs the religion. By the One in Whose Hand is my soul! You will not enter Paradise until you believe, and you will not believe until you love each other. Shall I tell you about what will strengthen that for you? Spread the Salam among each other."