[93] On which account the man who is going to take an oath ought to investigate everything with care and exceeding accuracy, considering whether the subject is of serious importance, and whether it has really taken place, and whether, if it has, he has comprehended it properly; and considering himself, also, whether he is pure in soul, and body, and tongue, having the first free from all violation of the law, the second from all defilement, and the last from all blasphemy.
For it is an impiety for any disgraceful words to be uttered by that mouth by which the most sacred name is also mentioned.