Oneness, Uniqueness of Allah (Tawheed)

Bukhari :: Book 9 :: Volume 93 :: Hadith 533

Narrated Anas bin Malik:

Allah's Apostle sent for the Ansar and gathered them in a tent and said to them, "Be patient till you meet Allah and His Apostle, and I will be on the lake-Tank (Al-Kauthar)."