João 18:17

The maid therefore that kept the door saith unto Peter, Art thou also one of this man's disciples? He saith, I am not. Now the servants and the officers were standing there, having made a fire of coals; for it was cold; and they were warming themselves: and Peter also was with them, standing and warming himself.

Art thou also ... indicates that John was openly known as a disciple of Jesus, and there is no evidence that Peter would have suffered any inconvenience by an open admission of his discipleship. However, it should be remembered that Peter had cut off Malchus' ear a little earlier; and, if his identity as the perpetrator of that act had been known, there would have been solid grounds for his arrest. If this entered into Peter's thinking, it would show how one wrong act inevitably leads to another wrong act. For full discussion of Peter's denials, see my Commentary on Matthew, Matthew 26:58.

Warming himself ... at the devil's fire was another circumstance in the chain of events leading to the denial.