Musnad Ahmad 31:371

Mu'awiyah narrated to us, Shayban narrated to us, from Firas, from 'Atiyyah, from Abu Sa'id, who said: The Prophet of Allah, may Allah bless him and grant him peace, said: "Whoever draws near to Allah by a span, Allah draws near to him by a cubit. And whoever draws near to Him by a cubit, Allah draws near to him by an arm's span. And whoever comes to Him walking, Allah comes to him at a run."