Even though the proverb was not posted here, this question is still perfectly answerable.
Answer:
The rhetorical device Twain uses by referencing a well-known proverb is allusion.
Explanation:
<u>Allusion is a figure of speech in which a reference is made to something or someone that has significance. The author does not explain much, since he/she assumes the audience knows who or what he/she refers to. </u>
<u>For instance, if someone says a woman is as beautiful as Helen of Troy, we would understand he/she means that woman is extremely beautiful. Helen of Troy is a famous character from the </u><u><em>Iliad</em></u><u>, by Homer, and she was the most beautiful woman in the world. The person making the allusion will not explain this fact, since it is well know.</u>
Therefore, if Twain is referring to a well-known proverb, he is making an allusion to it.