The Prophet (peace and blessings be upon him) said:
"The best slave (to set free) is the one whose price is highest and who is the most excellent and valuable in the eyes of his owners."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 1105
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[حم ق ن هـ] عن أبي ذر [حم طب] عن أبي أمامة.