A slave came and pledged allegiance to the Prophet ﷺ for hijrah, and the Prophet ﷺ did not realize that he was a slave. Then his master came looking for him.The Prophet ﷺ said to him, "Sell him to me."So he bought him for two black slaves. After that, he would not accept anyone's pledge until he had asked whether the person 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؟