Matthew 12:38-42
38 Then some of the scribes and Pharisees said to Him, “Teacher, we want to see a sign (attesting miracle) from You [proving that You are what You claim to be].”
39 But He replied and said to them, “An evil and adulterous generation [that is morally unfaithful to God] craves and demands a [miraculous] sign; but no sign will be given to it except the sign of the prophet Jonah; 40 for just as Jonah was three days and three nights in the belly of the sea monster, so will the Son of Man be three days and three nights in the heart of the earth. 41 The men of Nineveh will stand up [as witnesses] at the judgment against this generation, and will condemn it because they repented at the preaching of Jonah; and now, something greater than Jonah is here. 42 The Queen of the South (Sheba) will stand up [as a witness] at the judgment against this generation, and will condemn it because she came from the ends of the earth to listen to the wisdom of Solomon; and now, something greater than Solomon is here.
Luke 11:29-32
29 Now as the crowds were increasing [in number], He began to say, “This [present] generation is a wicked generation; it seeks a sign (attesting miracle), but no sign will be given to it except the sign of Jonah [the prophet]. 30 For just as Jonah became a sign to the people of Nineveh, so will the Son of Man also be [a sign] to this generation. 31 The Queen of the South (the kingdom of Sheba) will rise up in the judgment with the men of this generation and condemn them, because she came from the ends of the earth to listen to the wisdom of Solomon, and look, something greater than Solomon is here. 32 The men of Nineveh will stand up [as witnesses] at the judgment with this generation and condemn it, because they repented at the preaching of Jonah, and look, something greater than Jonah is here.