Hadith: None of you should say: O Allah, forgive me if You will; O Allah, be Merciful to me if You will; but he should appeal to Allah with determination, for nobody can force Allah to do something against His will
عن أبي هريرة رضي الله عنه مرفوعاً: «لا يَقُلْ أحدُكم: اللهم اغفِرْ لي إن شِئْتَ، اللهم ارحمني إن شِئْتَ، لِيَعْزِمِ المسألةَ، فإن الله لا مُكْرِهَ له».
ولمسلم:«وَلْيُعَظِّمِ الرَّغْبَةَ، فإن الله لا يَتَعَاظَمُه شيءٌ أعطاه». [صحيح] - [متفق عليه] المزيــد ...
Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: ''None of you should say: 'O Allah, forgive me if You will; O Allah, be Merciful to me if You will;' but he should appeal to Allah with determination, for nobody can force Allah to do something against His Will."
In another narration by Imām Muslim: "and let him ask Allah for whatever he wishes (no matter how great), for nothing is too great for Allah to give.” Sahih/Authentic. - [Al-Bukhari and Muslim]
Since all of Allah's slaves are in constant need of Him, and Allah is the Provider, the One worthy of all Praise, and the One who does what He wills, the Prophet (may Allah's peace and blessings be upon him) forbade the person who wants to supplicate Allah for forgiveness and mercy from saying: 'O Allah, forgive me if You will; be merciful to me if You will.' Rather, he commanded firmness and resoluteness in asking Allah, without the conditional "if You will", because saying this when requesting something from Allah implies that Allah is burdened by some of what His slaves ask Him for, or that something compels Him to fulfill it, which is not true. It may also imply the slave's lack of enthusiasm and that he is not in need of his Lord, whereas he cannot be without need of Allah for the blink of an eye. This also contradicts the neediness of the slave to Allah which is the essence of supplication. Moreover, giving Allah the choice to do something or not by saying "if You will" is unbefitting of Him, since no one or nothing can compel Him to do something. Then the Prophet (may Allah's peace and blessings be upon him) commanded the worshiper to be persistent in supplicating Allah, and to ask Him for whatever he wants of goodness whether it is much or little, for, indeed, nothing is difficult for Allah to give, and nothing is too great for Him to grant. Allah is the Sovereign of this world and the Hereafter; He has absolute control over them, and He has power over all things.