Abu Hurairah narrates fromRasool-Allah , "When anyone of you does duaa then don't say "Oh Allah! Forgive me if you want","Have mercy on me if you want", "Give me subsistence if you wish" rather believe completely that HE will do whatever HE wishes. Nobody can force HIM." (Bukhari)
Abu Hurairah narrates fromRasool-Allah , "Allah excepts the duaa of a person till the duaa is not related to sin or breaking of some relation and until he does not haste in that duaa. The people (May Allah be happy with them) asked, "Oh Rasool-Allah! What is meant by haste?" He replied, "That the person say "I did duaa again and again but my duaa wasn't accepted and afterwards he becomes hopeless and leaves the duaa. This is called haste." (Muslim)