A slave came and pledged allegiance to the Prophet ﷺ on emigration, without the Prophet ﷺ realizing that he was a slave. Then his master came looking for him, so the Prophet ﷺ said to him, "Sell him to me." He bought him in exchange for two black slaves, and after that he would not accept anyone's pledge of allegiance until he had asked whether he was a slave.
جاء عبد، فبايع النبي ﷺ على الهجرة، ولم يشعر أنه عبد، فجاء سيده يريده، فقال له النبي ﷺ: بعنيه. فاشتراه بعبدين أسودين، ثم لم يبايع أحدا بعد حتى يسأله أعبد هو؟