Berachos2: 7
וּכְשֶׁמֵּת טָבִי עַבְדּוֹ, קִבֵּל עָלָיו תַּנְחוּמִין. אָמְרוּ לוֹ תַלְמִידָיו: לֹא לִמַּדְתָּנוּ, רַבֵּנוּ, שֶׁאֵין מְקַבְּלִין תַּנְחוּמִין עַל הָעֲבָדִים? אָמַר לָהֶם: אֵין טָבִי עַבְדִּי כִּשְׁאָר כָּל הָעֲבָדִים; כָּשֵׁר הָיָה.
And when Tavi his slave died, he accepted condolences for him. His students said to him: Did you not teach us, our master, that we do not accept condolences for slaves? He said to them: Tavi my slave is not like all other slaves; he was a worthy [person].