Here's how:
* The Title: The title itself is an allusion. "The Gift of the Magi" refers to the biblical story of the three wise men who brought gifts to the newborn Jesus. This alludes to the theme of sacrifice and selfless love that's central to O. Henry's story.
* The Magi: The characters, Jim and Della, are presented as wise and resourceful, much like the biblical Magi. Their gifts, though simple, represent their deep love and understanding of each other.
* "The world had been made for them." This statement alludes to the romantic ideal of love conquering all and creating a perfect world for the lovers. This is a common theme in literature, particularly in stories about love and sacrifice.
While the story doesn't directly quote or reference any specific external source, the implied allusions contribute to the story's themes and overall meaning.