Al-Balawi (may Allah have mercy on him) narrates from Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "If slavery were established upon anyone of the Arabs, it would be so today; it is only captivity or ransom."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17490