Faith, or believe in Allah contains 4 elements (See: Syarah Ushulil Iman, page no. 13-22), which are:
First: Believe in the concrete form and existence of Allah the Exalted
The existence of Allah has long been proved by the fitra (pure character) of mankind, their intelligence, their five senses, and by shari’ah.
Evidence from fitra
Characteristically, mankind have already acknowledged the existence of the creator, the arranger, and the owner of this universe. No one deny this fact but the arrogant atheists. The Messenger of Allah -peace and blessings of Allah may be upon him-, “There is no child who is not born in a state of Fitrah, then his parents make him a Jew, or a Christian, or a Magian.” (Collected by Bukhari, in hadith no. 1292)