The Messenger of Allah ﷺ said, "Whoever frees his share in a slave is required to complete the emancipation by paying a fair valuation."
حدثنا هشيم أنبأنا يحيى بن سعيد عن نافع
أن رسول الله ﷺ قال من أعتق نصيبا له في مملوك كلف أن يتم عتقه بقيمة عدل
Its isnad is sahih. It has already been mentioned with the same meaning, in fuller form, among the hadiths following Musnad Umar 397, from the route of Malik from Nafi. It was narrated by the authors of the six books and others. See al-Muntaqa 3380–3386.