Musnad Ahmad 32:347

Hajjaj narrated to us, Shu'bah narrated to us, he said: I heard Qatadah narrating from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Your Lord says: 'When the servant draws near to Me by a span, I draw near to him by a cubit; and when he draws near to Me by a cubit, I draw near to him by an arm's length. And if he comes to Me walking, I come to him running.'"