Story within a story

A story told, staged, or written inside the work itself, which mirrors or comments on the main story.

In The Master and Margarita

I witnessed all this personally. I was on the veranda with Pontius Pilate, in the garden, when he spoke with Caiaphas; I was also on the rostrum, only secretly, incognito

By saying "I witnessed all this personally," the foreigner declares himself a witness to the story of Pilate that he has just told, and sews the account of Yershalaim into the conversation in Moscow, as if they were a single thread.

Part One, Chapter 3: The seventh proof, The foreigner (Woland)

You are free! You are free! He is waiting for you!

Part Two, Chapter 32: Forgiveness and eternal refuge, The Master