If the infinitely wise and all-knowing god of the Bible exists, then that god obviously would have been smart enough to know that Bible readers would understand that Jesus was completely alone as he prayed at Gethsemane, so no one could have overhead his prayer.
Thus, God would know that readers would conclude that Mark's story was at least part fiction. Now, if the words in Mark are from God, then we may presume that God did not want readers to think Mark just made them up, so God would have instructed Mark to explain to his readers that God told him what words Jesus used in his prayer. Since Mark did not do this, we may conclude that God did not help Mark write his gospel.
If God didn't tell him, then how did Mark decide what words to have Jesus say in his prayer? The answer to this question is found in the accounts of the life of King David, who was said to be the spiritual ancestor of the coming savior. Mark believed that some of the events in the life of David were foreshadowings of events in the life of the coming savior, so Mark made sure that Jesus' life mirrored in part the life of David. Thus, when Mark read David's lament about an enemies at his supper table,
You prepare a table before me in the presence of my enemies. (Psalm 23:5)
he made sure that Jesus likewise had an enemy sit at his last supper:
When evening came, Jesus arrived with the Twelve. While they were reclining at the table eating, he said, "I tell you the truth, one of you will betray me (Mark 14:17-20)
The parallel Mark constructed between David and Jesus doesn't end there. Mark also saw in the Scriptures that David was betrayed by someone close to him, someone who dipped his bread in the bowl with David:
David's counselor…is among the conspirators… (2 Samuel 15:12, 31)…. Even my close friend, whom I trusted, he who shared my bread, has lifted up his heel against me." (Psalm 41:9)
Since Mark felt sure that it was preordained that someone close to Jesus-- someone who shared bread with Jesus--would conspire against him, he made sure it happened:
"I tell you the truth, one of you will betray me--one who is eating with me…one who dips bread into the bowl with me." (Mark 14:17-20)
After learning of his betrayal by his counselor, David goes to the Mount of Olives and expresses his feeling that God's will for him will be done:
"let him [God] do to me whatever seems good to him." (2 Samuel 15:25-26)… David continued up the Mount of Olives (2 Samuel 15:30)
Mark wanted the same thing to happen to Jesus. After Mark has Jesus speak of his betrayal, Mark sends Jesus to Mt. of Olives to pray, just as did David after his betrayal:
they went out to the Mount of Olives. (Mark 14:26)…[and Jesus told God,] "Yet [do] not what I will, but what you will." (14:36)
Thus, nobody heard Jesus' prayer--if there was a prayer, and God did not tell Mark what Jesus said in the prayer. What actually happened, the evidence shows, is that Mark just assumed that the events following David's betrayal would have to be echoed a thousand years later in the life of Jesus. Following the betrayal by a friend that Mark manufactured for Jesus, Mark had Jesus travel up to the Mount of Olives, just as David did, and express the view that God would do with him what it was God's will to do, just as did David.
The words of Jesus' Gethsemane prayer were put there by Mark, and are complete fiction.
There are many more parallels between David's and Jesus' betrayals that Mark included in his narrative, but I'll leave those for interested readers to pursue. These parallels are described in considerable detail in the article, "David and Jesus," on the web page in the signature below.
Joseph F. Alward
"Skeptical Views of Christianity and the Bible"
* http://members.aol.com/jalw/joseph_alward.html