"an evil and adulterous generation seeketh after
a sign" Jesus said. But He did tell them that they
would be given a sign. "Destroy this temple and
in three days I will raise it up" John 2:19

Matthew 12:40 (in different words) "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"