Musnad Abu Ya'la al-Mawsili 115:340

Abu Musa narrated to us, Muhammad bin Ja'far narrated to us, Shu'bah narrated to us, he said: I heard Qatadah narrating from Anas bin Malik, that the Messenger of Allah (ﷺ) said: "Your Lord, Blessed and Exalted is He, says: 'If the servant draws near to Me by a span, I draw near to him by a cubit. And if he draws near to Me by a cubit, I draw near to him by an arm's span. And if he comes to Me walking, I come to him rushing.'"