Reference for Bava Batra 5:2
הַמּוֹכֵר אֶת הַחֲמוֹר, לֹא מָכַר כֵּלָיו. נַחוּם הַמָּדִי אוֹמֵר, מָכַר כֵּלָיו. רַבִּי יְהוּדָה אוֹמֵר, פְּעָמִים מְכוּרִין וּפְעָמִים אֵינָן מְכוּרִין. כֵּיצַד, הָיָה חֲמוֹר לְפָנָיו וְכֵלָיו עָלָיו, וְאָמַר לוֹ מְכוֹר לִי חֲמוֹרְךָ זֶה, הֲרֵי כֵלָיו מְכוּרִין. חֲמוֹרְךָ הוּא, אֵין כֵּלָיו מְכוּרִין:
One who sells an ass has not sold its gear. R. Nachum Hamadi says: He has sold its gear. [With riding gear, such as saddle and (saddle) cushion, all agree that he acquires them, even if they are not on it at the time of the sale. Where do they differ? With carrying gear, such as sack and (saddle) bags. The first tanna holds that he has not sold him the latter, and Nachum Hamadi holds that he has. The halachah is in accordance with the first tanna, viz.: he has not acquired the carrying appurtenances, even if they were not on it at the time of the sale.] R. Yehudah says: They are sometimes sold and sometimes not sold. How so? If an ass were (standing) before him with its gear on, and he said to him: "Sell me this ass" [implying: as it is, with its gear], its gear is sold. (If he said:) "Is it your ass?" [connoting: (If it is,) sell it to me, then it is as if he sells an ass itself, and] its gear is not sold, [even if it were upon it at the time of the sale. The halachah is not in accordance with R. Yehudah.]