In Brachot 49a, it talks about what people must say in birkat hamazon.
The top of the page is part of a braita, which quotes רבי אבא as saying that to fulfill their obligation, one must mention, among other things, brit milah and the Torah in the bracha on the land (נודה לך), and malchut David in the next bracha.
The Gemara then says this supports רבי אילעא אמר רבי יעקב בר אחא משום רבינו, who says the same thing.
When i learned this, i heard something interesting. Both the רבי אבא of the braita and רבינו of the Gemara are the same person - the man commonly known as רב. The source for רבי אבא is in the mesoret hashas gloss. ArtScroll brings Rashash as the source for רב being called רבינו.
I don't think רבינו here refers to רבי יהודה הנשיא, because he is usually called רבינו הקדוש when not referred to as רבי.
If that is the case, that they are the same person, what does the Gemara gain by bringing both statements of רב, under two names?