Tractate Berakhot - Chapter 2 - Mishnah 7 - Mishnah translated into english
When Tabi his [Rabban Gamaliel’s] slave died he accepted condolences for him. His disciples said to him: Master, have you not taught us that one does not accept condolences for slaves? He replied to them: My slave Tabi was not like other slaves: he was a fit man.