Luke 11:29

But the sign of Jonas. Instead of a prodigy in the heavens or in the air, I will give you one in the bosom of the earth, more wonderful than that of the prophet Jonas, who came out alive from the belly of the fish, which had swallowed him. Thus I will return alive from the bosom of the earth three days after my death. (Calmet) --- He gave them a sign, not from heaven, for they were unworthy to behold it, but from the deep; the sign of his incarnation, not of his divinity; of his passion, not of his glory. (Ven. Bede)