It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: When any one of you makes supplication, he should not say, "O Allah, if You will, forgive me; have mercy on me," but he should supplicate with determination and certainty, for there is no one who can compel Allah.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 10867