It was narrated from Umar Ibnul Khattaab (radiyallaahu-anhu) that he said:

”Indeed, I do not preoccupy myself with the response to (a supplication), but I preoccupy (myself) with the supplication (itself); for if I preoccupy myself with the supplication, then indeed the response is (attached) to it.”

[Source: Iqtidaa Siraat Al-Mustaqeem 2/706]