In The Strange Case of Dr. Jekyll and Mr.Hyde, is there an example of an allusion in the first chapter?

An allusion is when an author refers
to another work of literature or art.

In the beginning of
Dr. Jekyll and Mr. Hyde, Robert Louis Stevenson describes one of
the main characters in the story, Mr. Utterson.  When one of his friends got himself
into trouble, Mr. Utterson "was inclined to help rather than to
reprove."

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"I incline to Cain's heresy," he used
to say quaintly:  "I let my brother go to the devil in his own
way."

This is an allusion to
the Biblical story of Cain and Abel, found in the book of Genesis, Chapter 4.  Cain and
Abel are two sons of the first humans, Adam and Eve.  Like many brothers who came after
them, Cain and Abel quarrel, and Cain kills his brother, becoming the world's first
murderer.  When God asks Cain, "Where is Abel your brother," Cain replies, "I do not
know; am I my brother's keeper?"

This answer is,
understandably, usually interpreted as a cynical, cruel remark; after all, Cain himself
murdered Abel, so it is no excuse to claim that he is not responsible for his brother's
safety.

Mr. Utterson refers to this cynical, cruel answer
as "Cain's heresy."  What he means by this is rather an interesting twist.  Whereas Cain
truly did not care about his brother, Mr. Utterson truly does care about his friends. 
It's just that he does not rebuke them for their misbehavior which creates problems for
them.  Rather, he helps them.

Mr. Utterson displays this
trait later in the story when he remains faithful to his friend Dr. Jekyll even after
his behavior has become strange and other friends have abandoned
him.