Sahih Muslim Book 35, Hadith Number 6496.
Chapter : Merit of remembrance of Allah and calling Him, and nearness to Allah, the Exalted.
Abu Huraira reported Allah’s Apostle (may peace be upon him) as saying that Allah, the Exalted and Glorious, said: When My servant draws close to Me by the span of a palm, I draw close to him by the cubit and when he draws close to Me by the cubit, I draw close to him by the space (covered) by two hands, and when he draws close to Me by the space (covered) by two hands, I go in hurry towards him.