Al-Sha'bi (may Allah have mercy on him) says that when Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) delivered a sermon, he said: An Arab is not anyone's property, and we will not snatch from a man's hand anything he held when he accepted Islam; but we will fix his value at five camels.
Abu Ubayd (may Allah have mercy on him) says: When someone holds a captive in his hand, we will not take him without compensation, because he accepted Islam while holding him; nor will we let him remain a slave, because he is an Arab; rather, the one who enslaved him will be paid a value of five camels, and the Arab will return to his lineage.
This narration from Sayyiduna Umar (may Allah be pleased with him) is munqati' (broken).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18069