Sahih Muslim
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)
Book Number: 035 / Hadith Number: 6495
Abu Huraira reported Allah's Messenger (may peace be upon him as saying that Allah thus stated: I live in the thought of My servant as he thinks of Me and with him as he calls Me.