Matthew 12:38-40

Then certain of the scribes and of the Pharisees answered, saying, Master, 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 the prophet Jonas: for as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.