After this, as though his object was to swell the size of his book, he advises us “to choose Jonah rather than Jesus as our God;” thus setting Jonah, who preached repentance to the single city of Nineveh, before Jesus, who has preached repentance to the whole world, and with much greater results. He would have us to regard as God a man who, by a strange miracle, passed three days and three nights in the whale's belly; and he is unwilling that He who submitted to death for the sake of men, He to whom God bore testimony through the prophets, and who has done great things in heaven and earth, should receive on that ground honour second only to that which is given to the Most High God.
Moreover, Jonah was swallowed by the whale for refusing to preach as God had commanded him; while Jesus suffered death for men after He had given the instructions which God wished Him to give. Still further, he adds that Daniel rescued from the lions is more worthy of our adoration than Jesus, who subdued the fierceness of every opposing power, and gave to us “authority to tread on serpents and scorpions, and over all the power of the enemy.” Finally, having no other names to offer us, he adds, “and others of a still more monstrous kind,” thus casting a slight upon both Jonah and Daniel, for the spirit which is in Celsus cannot speak well of the righteous.
Source: Against Celsus (New Advent)