Question 161.
How did mankind realize that Allah is One? ?

Answer 161.
For one thing, man’s reason (provided it is sound) affirms that Allah is One. Hence all men of wisdom, all great scholars of the world, have had belief in the Oneness of Allah. Secondly, the prophets of Allah have unanimously given mankind the creed of the Oneness of Allah and told them that Allah is One and none else is like unto Him.