Who recorded it?
Jesus is in the garden with Peter, James and John but he removes himself from them and prays alone. In all three accounts of this event we read that the disciples fell asleep and Jesus had to actually wake them up. So if Peter, James and John were all sleeping, and that at some distance away, who heard the words of Jesus prayer so as to record it?
Jesus himself couldn't have recounted the prayer to them, he was arrested and taken away in one quick, fell swoop and never spoke to those disciples ever again except perhaps for a few words while dying when he entrusted his mother into the care of a discple who may have been John.
So again, who recorded this prayer?