Malik related to me from Hisham ibn Urwa from his father from A'isha, the wife of the Prophet ﷺ that the Messenger of Allah ﷺ was asked what was the most excellent kind of slave to free. The Messenger of Allah ﷺ answered, "The most expensive and the most valuable to his master."

حَدَّثَنِي مَالِكٌ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، زَوْجِ النَّبِيِّ ﷺ أَنَّ رَسُولَ اللَّهِ ﷺ سُئِلَ عَنِ الرِّقَابِ أَيُّهَا أَفْضَلُ فَقَالَ رَسُولُ اللَّهِ ﷺ " أَغْلاَهَا ثَمَنًا وَأَنْفَسُهَا عِنْدَ أَهْلِهَا " .