JMNT(i)
38 At that point some of the scribes (scholars; theologians; experts of the Law) and the Pharisees gave a calculated response to Him, one after another, saying, "Teacher, we continue wanting to see a sign from you!"
39 So He, making a decided reply, said to them, "A good-for-nothing, worthless, base, knavish, grievously oppressive and wicked – even adulterous (unfaithful and immoral) – generation repeatedly seeks intently for a sign! And yet a sign will not proceed to be given to it – except the sign of Jonah the prophet.
40 "You see, just as Jonah was within the midst of the belly of the huge fish (or: sea monster) [for] three days and three nights [Jonah. 1:17], thus in this way will the Son of the Man (humanity's son; = Adam's son) continue being within the heart of the earth [for] three days and three nights.