This Is Not My Life to Take

Alice, the villain, will be taunting Bob, the hero for being too cowardly to take her life and Bob's response is along the lines of: "It's not mine to take", as he sheathes his weapon (or hands it to another character). The motive is usually The Only One Allowed to Defeat You (because the speaker recognizes he/she is not said "Only One). It could be said during a Sword Over Head moment, but not every Sword Over Head moment uses this phrase.

Comic Books:

 * In Buffy the Vampire Slayer: Season Eight near the end of issue #15 ("Wolves At The Gate, Part IV"), where Dracula cripples the leader of the vampire army, who screams at Dracula to let him die with honor. Dracula tells the crippled vampire that he knows nothing of honor, and that he is not Dracula's to kill--after which he hands his sword to Xander, whose girlfriend the vampire leader had murdered. Xander delivers the coup de grace, then breaks down as Buffy comforts him and the battle continues.

Film:
"Miraz: What's the matter boy? To cowardly to take a life?
 * In the 2008 The Chronicles of Narnia: Prince Caspian, Miraz, Caspian's uncle, who murdered Caspian's father, and was planning to do the same to Caspian...is defeated in a duel by Peter. Miraz wonder's why Peter won't kill him, Peter nearly saying the trope word for word, before handing his sword to Caspian.

Peter: It's not mine to take."


 * Although not a death, something similar to this is subverted in Mc Lintock!. John Wayne's character is thoroughly pissed at another character who almost hung an innocent man, and after giving him a good chewing out, says, "Somebody ought to hit you. But I'm not going to hit you. I'm not going to hit you. (beat) Oh, the hell I'm not" and slugs him.

Literature:

 * In Harry Potter, Harry gives Griffindor's magical sword to his best friend Ron to destroy a plot important locket, which has part of the soul of the Big Bad inside of it.
 * In Prisoner of Azkaban, Black and Lupin give Harry the choice of whether the man who was responsible for giving away Harry's parents' location to their murderer should live or die.

Video Games:

 * Can be played straight or averted with Mass Effect 2. Pretty much every loyalty mission that comes with a distinct "Kill this person" ending, can have the players Shepard kill the target, have Shepard convince their team-mate to kill the target, or not kill the target at all.
 * Can be played straight in Dragon Age, too. At the Landsmeet,.
 * Similarily, at the end of the Leliana's Song DLC, Leliana refrain from killing Harwen Raleigh, leader of the Hard Line mercenaries. Instead, she can allow her comrade Silas, who was tortured for several months in Raleigh's dungeons, to finish him off.
 * And in Knights of the Old Republic, the protagonist leaves Admiral Karath to Karth, since Its Personal, and may or may not (depending on morality) encourage Juhani to take revenge on the man who bought her as a 'pet'.... Let's just say Bioware loves this trope.
 * In Alpha Protocol, Mike has the option . In this case it's an intentional case of sadism, as his death will become infinitely much more painful than if Mike just puts a bullet through his head.

Web Comics

 * In Order of the Stick, Belkar, of all people, does this here and here.
 * In Escape From Terra, a family is killed by invaders, leaving one survivor (a teenage girl), and the man who gave the order captured. When he taunts the man in charge about whether he has the balls to kill him and face the consequences from his superiors, the man explains that it's not up to him and gives his gun to the girl.

Western Animation:

 * In Avatar: The Last Airbender, Prince Zuko refrains from killing his father, Fire Lord Ozai, out of recognition that he is not the person who should kill Ozai.