36 Simon Peter said to Him, “Lord, where are You going?”
Jesus answered him, “Where I am going you cannot follow Me now, but you shall follow Me afterward.”
37 Peter said to Him, “Lord, why can I not follow You now? I will lay down my life for Your sake.”
38 Jesus answered him, “Will you lay down your life for My sake? Most assuredly, I say to you, the rooster shall not crow till you have denied Me three times.” — John 13:36-38.
Peter wants to know where Jesus is going. Jesus indicates that Peter cannot follow Him [to the Cross and death] now but he would follow later. Despite Peter’s spontaneous and extravagant claim that he would lay down his life for Jesus, Jesus tells him that He knows that Peter would deny Him three times very soon [before dawn].