This comic refers to the scene in The Fellowship of the Ring (extended edition DVD: 1:31:45) where Elron tells Gandalf that he witnesses Isildur standing over the fires of Mnt. Doom. Elrond says: “I led Isildur into the heart of Mount Doom, where the ring was forged, the one place where it could be destroyed…

“Cast it into the fire! Destroy it!”

“No.”

“It should’ve ended that day, but evil was allowed to endure.”

[Source: @jholtillus]