Berachos, Chapter 4, Mishnah 7. This Mishnah addresses the question of whether the Mussaf prayer was instituted to be said only with a congregation, or by an individual as well.
"Rabbi Elazar ben Azaryah omer: ein tefillas ha'musafin ela b'chever ir" - 'chever ir' is another term for a congregation and a community. According to Rabbi Elazar ben Azaryah, an individual praying on his own cannot recite the Mussaf prayer, since this prayer was instituted specifically to be said with a congregation.
"V'chachamim omrim: b'chever ir v'shelo b'chever ir" - the Sages disagree and rule that the Mussaf prayer is said both with a congregation and not with a chever ir, that is, even by an individual, and this is our practice today.
Rav Yehudah's approach in understanding Rabbi Elazar ben Azaryah's words:
"Rav Yehudah omer mishmo: kol makom sheyesh chever ir - hayachid patur mitefillas ha'musafin" - Rav Yehudah explains Rabbi Elazar ben Azaryah's words differently from the straightforward understanding of the first Tanna's statement: wherever there is a chever ir, that is, a congregation, the individual is not required to pray on his own, but may listen to the chazzan, who exempts him and fulfills his obligation on his behalf.
According to this understanding, Rabbi Elazar ben Azaryah would hold that when there is no congregation, the individual is obligated to pray Mussaf on his own. His entire statement comes only to teach that when a person is together with the community, the chazzan who leads the prayer includes him in his own prayer, and he is not required to recite the Shemoneh Esrei of Mussaf himself.
In summary: this Mishnah presents a dispute about the individual's obligation in the Mussaf prayer. According to the plain meaning of Rabbi Elazar ben Azaryah's words, the Mussaf prayer is said only with a congregation; according to the Sages, it is said both with a congregation and by an individual alike; and according to Rav Yehudah in his name, where there is a congregation the individual is exempt and fulfills his obligation by listening to the chazzan, but in the absence of a congregation he must pray on his own.