Power of Du'a

In al-Qur'an, Allah Subhanahu wa Ta'ala says

"When My servants ask about Me, I am indeed close to them. I listen to the prayer of every supplicant, when he calls on Me. Let them also, with a will, listen to My call, and believe in Me, so that they may walk in the right way"

{Al-Qur'an 2:186}