Hazrat Shurayh (may Allah have mercy on him) says that due to foolishness (a slave girl or slave) will be returned.

Hazrat Zaid Abu al-Ma'la (may Allah have mercy on him) narrates that I was present with Hazrat Iyas bin Mu'awiyah (may Allah have mercy on him), when a dispute regarding a slave girl was brought before him. One person said, "I bought this slave girl from him, but she is foolish." The other said, "I do not know that she would be returned due to foolishness." The first person submitted, "Foolishness is also like insanity." Hazrat Iyas (may Allah have mercy on him) asked the woman (slave girl) in Persian, "Do you remember the night in which you were born?" She replied, "Yes." He (may Allah have mercy on him) asked her, "Which of your legs is longer?" She pointed to one leg and said, "This one." Thus, she was returned to her previous owner.

Hazrat Aamir (may Allah have mercy on him) says that a return will not be made due to minor foolishness or ignorance, but if the foolishness is like madness, then it will be returned.