Matthew 12:38-40

Then certain of the scribes and Pharisees answered him, saying, Teacher, we would see a sign from thee. But he answered and said unto them, An evil and adulterous generation seeketh after a sign; and there shall no sign be given to it but the sign of Jonah the prophet: for as Jonah was three days and three nights in the belly of the whale; so shall the Son of man be three days and three nights in the heart of the earth.