Oneness, Uniqueness of Allah (Tawheed)

Bukhari :: Book 9 :: Volume 93 :: Hadith 569

Narrated Abu Huraira:

The Prophet said, "None of you should say: 'O Allah! Forgive me if You wish,' or 'Bestow Your Mercy on me if You wish,' or 'Provide me with means of subsistence if You wish,' but he should be firm in his request, for Allah does what He will and nobody can force Him (to do anything)."