In the Holy Bible, Jesus is using an example of Jonah when he was in the belly of a great fish and it says in Matthew 12:40,
Jesus said, "For as Jonah was in the belly of the great fish for three days and three nights, so will the Son of Man be in the heart of the earth for three days and three nights.”
Son of Man is Jesus, God's only Son.
I hope this answers your question and God bless! :)