Mark 9:13
But I say unto you, That Elias is indeed come, and they have done unto him whatsoever they listed, as it is written of him.
Cross-reference
In Mark 6:14-28, the account of John’s beheading details the suffering Jesus refers to — 'they did to him whatever they wished'.
Matthew 11:14 explicitly identifies John the Baptist as Elijah, confirming Jesus' statement that Elijah has come.
In Matthew 14:3-11, the parallel narrative of John’s imprisonment and beheading provides the specific events behind Jesus' words.
In Matthew 17:12, the parallel account directly echoes Jesus' statement that Elijah has come and suffered, reinforcing the identification of John as Elijah.
In Matthew 17:13, the disciples realize Jesus was speaking about John the Baptist, clarifying the identification of Elijah with John.
In Luke 1:17, John is prophesied to go before the Lord in the spirit of Elijah — the very fulfillment Jesus declares in Mark 9:13.
In Matthew 14:10, John is beheaded — the specific outcome of the suffering Jesus alludes to in Mark 9:13.
In Luke 3:19, John rebukes Herod, initiating the conflict that leads to his imprisonment — the cause of the suffering referenced.
In Luke 3:20, John is imprisoned, a step toward his death — directly connecting to 'they did to him whatever they wished'.