Where did jesus say this? Is it recorded in the same gospel you're telling us to look to?
It's in the book of Matthew, ch12.
Then certain of the scribes and Pharisees answered, "
Teacher, we want to see a sign from you." But he answered them, "An evil and adulterous generation seeks after a sign, but no sign will be given it but the sign of Jonah the prophet.
For as Jonah was three days and three nights in the belly of the whale, so will the Son of Man be three days and three nights in the heart of the earth. The men of Nineveh will stand up in the judgment with this generation, and will condemn it, for they repented at the preaching of Jonah; and behold, someone greater than Jonah is here. The queen of the south will rise up in the judgment with this generation, and will condemn it, for she came from the ends of the earth to hear the wisdom of Solomon; and behold, someone greater than Solomon is here.
Again in John ch6
They said therefore to him, "
What then do you do for a sign, that we may see, and believe you? What work do you do? Our fathers ate the manna in the wilderness. As it is written, 'He gave them bread out of heaven to eat.'"
Jesus therefore said to them, "Most certainly, I tell you, it wasn't Moses who gave you the bread out of heaven, but my Father gives you the true bread out of heaven. For the bread of God is that which comes down out of heaven, and gives life to the world." They said therefore to him, "Lord, always give us this bread."
Jesus said to them, "I am the bread of life"