Full Sharh — Riyad as-Salihin 1064
عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: "لا يقولن أحدكم: اللهم اغفر لي إن شئت: اللهم ارحمني إن شئت، ليعزم المسألة، فإنه لا مكره له" ((متفق عليه)). ((وفي رواية لمسلم: "ولكن ليعزم، وليعظم الرغبة، فإن الله تعالى، لا يتعاظمه شيء أعطاه")).
English Translation
Abu Hurairah (May Allah be pleased with him) said:: The Messenger of Allah (ﷺ) said, "You must not supplicate: 'O Allah! forgive me if You wish; O Allah bestow mercy on me if You wish.' But beg from Allah with certitude for no one has the power to compel Allah."Another narration of Muslim is: "A supplication should be made in full confidence and one should persistently express his desire (before Allah) in his supplication, for no bounty is too great for Allah to bestow (upon his slaves)."
Source
Riyad as-Salihin(رياض الصالحين)
The Book of the Prohibited actions
Hadith Number
1064