It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that I heard the Noble Prophet (peace and blessings be upon him) say: "Whoever slaps his slave or beats him without fault, then its expiation is that he should set him free."
Hadith Referenceالادب المفرد / كتاب / 177
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه مسلم ، كتاب الإيمان : 1657 و أبوداؤد : 5168 - الإرواء : 2173»