Musnad Abu Ya'la al-Mawsili 5:4

Abu Khaythama narrated to us, Abu 'Amir al-'Aqadi narrated to us, from 'Ali ibn al-Mubarak, from Yahya ibn Abi Kathir, from Ya'ish ibn al-Walid, that a freed slave of the family of al-Zubayr narrated to him, from al-Zubayr, that the Messenger of Allah (may Allah bless him and grant him peace) said: "The disease of the nations before you has crept toward you: envy and hatred. It is the 'shaver' (haliqah); I do not mean the shaver of hair, but the shaver of the religion. By the One in whose hand is the soul of Muhammad, you will not enter Paradise until you believe, and you will not believe until you love one another. Shall I not inform you of that which will establish that for you? Spread the greeting of peace (salam) among yourselves."