Allah has guaranteed the response of the du’a of the one in distress, as He Himself informed us of this (guarantee). And the reason for this is that the one in distress will turn to him with a pure sincerity, cutting his hope off from all other sources. And sincerity to Him is in the cause of (gaining) His Protection, regardless of whether it emanates from a kafir or Muslim, evil or pious!

—Al-Qurtubī [d. 671H/1272CE]

al-Jami’ li Ahkam al-Qur’an, 13/223

(Read on pg 140, Yasir Qadhi, Du’a: The Weapon of the Believer. Al-Hidaayah Publishing & Distribution Ltd. Birmingham: 2003.)