Musnad Ahmad 3:66

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, he said: I heard Khalid, from Abu Bishr al-'Anbari, from Humran ibn Aban, from Uthman ibn Affan, from the Prophet, may Allah bless him and grant him peace, who said: "Whoever dies while he knows that there is no god but Allah, will enter Paradise."