Protagoras

As to the gods, I have no means of knowing either that they exist or do not exist.

Everyone, including the Athenians [...] are right to accept advice from anyone, since it is incumbent on everyone to share in that sort of excellence, or else there can be no city at all.

As to gods, I have no way of knowing either that they exist or do not exist, or what they are like.

Concerning the gods, I have no means of knowing either that they exist or that they do not exist, nor what sort of form they may have; there are many reasons why knowledge on this subject is not possible, owing to the lack of evidence and the shortness of human life.

Many things prevent knowledge, including the obscurity of the subject and the brevity of human life