Matthew 12:38-40: Then some of the scribes and Pharisees said to [Jesus], "Teacher, we wish to see a sign from you."  But he answered them, "An evil and adulterous generation asks for a sign, but no sign will be given to it except the sign of the prophet Jonah.  For just as Jonah was three days and three nights in the belly of the sea monster, so for three days and three nights the Son of Man will be in the heart of the earth.”