Oneness, Uniqueness of Allah (Tawheed)

Bukhari :: Book 9 :: Volume 93 :: Hadith 560

Narrated 'Ubada bin As-Samit:

I, along with a group of people, gave the pledge of allegiance to Allah's Apostle. He said, "I take your Pledge on the condition that you (1) will not join partners in worship with Allah, (2) will not steal, (3) will not commit illegal sexual intercourse, (4) will not kill your offspring, (5) will not slander, (6) and will not disobey me when I order you to do good. Whoever among you will abide by his pledge, his reward will be with Allah, and whoever commits any of those sins and receives the punishment in this world, that punishment will be an expiation for his sins and purification; but if Allah screens him, then it will be up to Allah to punish him if He will or excuse Him, if He will."