Sahih Muslim
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)
Book Number: 035 / Hadith Number: 6477
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.