Peter’s question was probably for John’s benefit, as a close friend (Acts 3:1) and in repayment for the favor John did for him at the supper (John 13:24). But Peter’s motives may have been less pure. He may have been shocked by Jesus’ prediction of suffering in his life and wanted to have some company in that misery, or plain old curiosity may have inspired the question. Whatever the case, the reply of Jesus seems to indicate that there was something wrong with Peter even asking such a thing.

Acts 3:1  One day Peter and John were going up to the temple at the time of prayer—at three in the afternoon.

John 13:24  Simon Peter motioned to this disciple and said, “Ask him which one he means.”