Caesar, Gallic War 5.6
Caesar is planning his second invasion of Britain; but the troublesome Dumnorix refuses to join him. Caesar records two of his excuses:
ille omnibus primo precibus petere contendit ut in Gallia relinqueretur, partim quod insuetus navigandi mare timeret, partim quod religionibus sese diceret impediri.
At first he strove to beg by every kind of entreaty that he should be left behind in Gaul, partly on the ground that, being unaccustomed to sailing, he was afraid of the sea, partly because he said that he was prevented by religious obligations.