Uthman ibn `Affan said: I heard Allah's Messenger say: "Verily, I know a phrase which no servant utters truthfully from his heart except the Fire is made unlawful for him." `Umar ibn al-Khattab said: "I shall tell you what that phrase is. It is the kalima of sincerity with which Allah has empowered Muhammad and his Companions, the kalima of fear of Allah which Allah's Prophet enjoined upon his uncle Abu Talib on his deathbed: the witnessing that there is no god but Allah." Ahmad related it in his Musnad (1:63 #449).