Sahih Bukhari Volume 009, Book 093, Hadith Number 502.

Narrated By Abu Huraira : The Prophet said, "Allah says: 'I am just as My slave thinks I am, (i.e. I am able to do for him what he thinks I can do for him) and I am with him if He remembers Me. If he remembers Me in himself, I too, remember him in Myself; and if he remembers Me in a group of people, I remember him in a group that is better than they; and if he comes one span nearer to Me, I go one cubit nearer to him; and if he comes one cubit nearer to Me, I go a distance of two outstretched arms nearer to him; and if he comes to Me walking, I go to him running.'"