Musnad Ahmad 30:3573

Rawh narrated to us, Zuhayr ibn Muhammad narrated to us, Zayd ibn Aslam narrated to us, from Abu Salih, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: Allah, the Almighty and Majestic, said: "I am as My servant thinks of Me, and I am with him when he remembers Me."