In the Anime "Cop Craft" this seems to be part of the honor code of "Knights of Mirvor."
Tilarna Exedilica gets told that she can't save her fairy friend without breaking earth laws, so she leaves her sword into a diner and disappears. Cop who is left with the sword, bewildered due to her previous comments about the weapon's importance, searches Bland Name version of Wikipedia for the magical world customs.
The wiki page within show itself◊
Short version: knight can go partially "go rogue" without dishonoring their order by leaving their sword to someone they trust.
EDIT: I remembered that this is similar to a thing that actual, historical knights did, temporarily becoming non-knights to perform actions that would go against the code of chivalry. Showcased here in 6.00 mark. (Horrible Histories has reputation of high historical accuracy.)
Edited by vatas
Moving this example off the page because it needs some clarification. Does Triton eventually start using the trident again? If not, then I'd say this counts. If he does, then this is more Dramatic Drop than this trope.