Sahih Muslim | Book 35 | Chapter 3

Narrated by Anas
Anas reported Allah's Messenger (may peace be upon him) as saying: When one of you makes supplication, he should supplicate with a will and should not say: O Allah, confer upon me if Thou likest, for there is none to coerce Allah.

Narrated by Abu Huraira
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: When one of you makes a supplication (to his Lord) one should not say: O Allah, grant me pardon, if Thou so likest, but one should beg one's (Lord) with a will and full devotion, for there is nothing so great in the eye of Allah which He cannot grant.

Narrated by Abu Huraira
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: None of you should say to Allah (like this): O Allah, grant me mercy, if thou so likest. The supplication (of his) should (be permeated with) conviction (that it would be accepted by the Lord), for Allah is the Doer of (everything) He likes to do, and there is none to force Him (to do or not to do this or that).