Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that Sayyiduna Salman al-Farisi (may Allah be pleased with him) narrated his story, and in it he said: A Jew from Banu Qurayzah came to Wadi al-Qura and bought me from the one with whom I was, and he brought me to Madinah. He narrated his story to the Prophet (peace and blessings be upon him), and when he finished, the Messenger of Allah (peace and blessings be upon him) said: "O Salman! Make a contract of manumission." So I made a contract of manumission.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21741