Musnad Ahmad 788:52

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Abu Bishr, from Sa'id ibn Jubayr, from Abu Musa al-Ash'ari, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever among my nation, or a Jew, or a Christian, hears of me and then does not believe in me, will not enter Paradise."