Reference for Sukkah 71:7

אמר מר אתרוג כושי פסול והתניא כושי כשר דומה לכושי פסול אמר אביי כי תנן נמי מתני' דומה לכושי תנן רבא אמר לא קשיא הא לן והא להו

The Master has said: An Ethiopian etrog is invalid. But has it not been taught: If it is Ethiopian it is valid, if it is like an Ethiopian, it is invalid? Abaye answered, In our Mishnah also we learned of one that is like an Ethiopian. Raba answered, There is no difficulty. The former refers to us, the latter to them.

Jastrow