Silsilah as-Sahihah 2876 — How Slaves and Masters Should Address Each

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "None of you should say to his slave «عبدي» (my servant), rather he should say «فتاي» (my attendant), for all of you are Allah's servants. Similarly, no slave should say to his master «ربى» (my lord), rather he should say «سيدى» (my chief)."