And therefore, if the historical evidence in the two cases is at all equal--or rather, if that which supports the more improbable account does not greatly preponderate--we ought to give credence to the more moderate and probable of the two statements.
Now, putting aside authors who merely re-echo the statements of others, there seem to be, in the present case, two and two only distinct original authorities--Herodotus and Ctesias.

Of these two, Herodotus is the earlier.

He writes within two centuries of the termination of the Assyrian rule, whereas Ctesias writes at least thirty years later.

He is of unimpeachable honesty, and may be thoroughly trusted to have reported only what he had heard.

He had travelled in the East, and had done his best to obtain accurate information upon Oriental matters, consulting on the subject, among others, the Chaldaeans of Babylon.