Oneness, Uniqueness of Allah (Tawheed)

Bukhari :: Book 9 :: Volume 93 :: Hadith 622

Narrated 'Aisha:

Whoever tells you that the Prophet concealed something of the Divine Inspiration, do not believe him, for Allah said: 'O Apostle Muhammad! Proclaim (the Message) which has been sent down to you from your Lord, and if you do it not, then you have not conveyed His Message.' (5.67)