Ibn Daylami (may Allah have mercy on him) says that once I went to meet Hazrat Ubayy ibn Ka'b (may Allah be pleased with him) and said, "O Abu'l-Mundhir! Some doubts about predestination have arisen in my heart. Please narrate to me a hadith by the blessing of which these doubts may be removed from my heart." He replied, "If Allah were to punish all the inhabitants of the heavens and the earth, even then He would not be unjust to them. And if He were to have mercy on them, His mercy would be greater than their deeds. And if you were to spend gold equal to Mount Uhud in the way of Allah, Allah would not accept it from you until you have complete faith in predestination, and until you are certain that whatever has come to you could not have missed you, and whatever has missed you could not have come to you. If you die holding any belief other than this, you will enter Hell."