Where and why are Damon and Pythias mentioned in 'Dr. Jekyll and Mr Hyde'?

Damon and Pythias are mentioned in "Dr. Jekyll and Mr Hyde" in a conversation between Dr. Jekyll and Mr. Utterson. Dr. Jekyll references them to explain his close friendship with Mr. Hyde and the concept of loyalty and sacrifice between friends. The reference highlights the contrast between the two characters and foreshadows the themes of duality and friendship explored in the novella.