Bukhari

Hadith Commentary:
Supplication (du'a) must be made with complete confidence and trust. It should be with the belief that Allah Ta'ala will certainly accept that supplication. Acceptance may occur quickly or after some delay, but the supplication will definitely bear fruit, as is evident from daily experiences.

Hadith Commentary:
A Muslim servant should supplicate with complete confidence and certainty.
He should make supplication with the belief that Allah Ta’ala will surely accept it.
It may be accepted quickly or after some delay, but it is never wasted; supplication will certainly have its effect.
Supplication should not be made conditional upon Allah Ta’ala’s will.
That is, one should not say: “If You will, then accept it.”
Doing so may give the impression that granting the request is possible without His will, whereas without will, it would be compulsion, and no one can compel Allah Ta’ala.
The use of “will” applies to one who can be forced to do something, and Allah Ta’ala is free from this.
In the hadith, the Messenger of Allah sallallahu alayhi wa sallam said:
“When making supplication, do not say: O Allah! If You will, forgive me; if You will, have mercy on me.
A person should supplicate with full determination and confidence; Allah Ta’ala does whatever He wills.
No one can compel Him to do anything.”
(Sahih Muslim, Kitab al-Dhikr wa’l-Du‘a, Hadith: 6813.
(2679)
Hafiz Ibn Hajar rahimahullah has written that Allah Ta’ala dislikes such conditional supplication because it carries a sense of indifference towards one’s own request, and even towards Allah Ta’ala Himself.
(Fath al-Bari: 13/557)