Umar Bin al-Khattab رضي الله عنه:
"I am not worried about whether my du’a will be responded to, but rather I am worried about whether I will be able to make du’a or not. So if I have been guided (by Allah) to make du’a, then (I know) that the response will come with it."
(Al-Awāyishah, pg. 117)