Oneness, Uniqueness of Allah (Tawheed)

Bukhari :: Book 9 :: Volume 93 :: Hadith 556

Narrated Anas:

Allah's Apostle said, "Whenever anyone of you invoke Allah for something, he should be firm in his asking, and he should not say: 'If You wish, give me...' for none can compel Allah to do something against His Will."