Captivity and Deliverance
According to the synaxarion, Peter prayed to Saint Nicholas the Wonderworker while imprisoned at Samara. Tradition relates that Saint Nicholas appeared to him and counselled him to invoke Saint Simeon the God-Receiver, and that the two saints together effected his release—Saint Simeon dissolving his chains and Saint Nicholas guiding him to Greek territory.
OrthodoxWiki notes that the prison of his captivity is identified by some accounts with the same fortress that later held the Forty-Two Martyrs of Amorion. Directed by Saint Nicholas, Peter is said to have travelled to Rome, where he received the monastic habit at the tomb of the Apostle Peter.