Pesachim 29A

דישראל נמי מישרא קא שרי! ואי רבי יוסי הגלילי ⁠— אפילו תוך זמנו נמי מישרא קא שרי בהנאה.

R' Shimon also permits one to derive benefit from leavened bread after Passover even if it was owned by a Jew. And if the Mishnah follows the opinion of R' Yosei HaGelili, he would permit one to derive benefit from it even during Passover.

אמר רב אחא בר יעקב: לעולם רבי יהודה היא, ויליף שאור דאכילה משאור דראייה. מה שאור דראייה ⁠— שלך אי אתה רואה, אבל אתה רואה של אחרים ושל גבוה. אף שאור דאכילה ⁠— שלך אי אתה אוכל, אבל אתה אוכל של אחרים ושל גבוה.

Rav Aḥa bar Ya’akov said: Actually, it is possible to explain that the Mishnah is in accordance with the opinion of R' Yehuda, and he derives the restrictions pertaining to the eating of leaven from the restrictions relating to seeing leaven. The prohibition against seeing leaven is worded: “It should not be seen by you.” It is understood to mean that you should not see your own or another Jew’s leaven. But you may see leaven that belongs to others, i.e., non-Jews, and leaven consecrated to God. Similarly, with regard to the prohibition against eating leaven that was owned by a Jew during Passover after Passover, you may not eat your own leavened bread, but you may eat the leavened bread of others or the leaven consecrated to God after Passover.

ובדין הוא דאיבעי ליה למיתנא דאפילו באכילה נמי שרי, ואיידי דתנא דישראל אסור בהנאה ⁠— תנא נמי דגוי מותר בהנאה. ובדין הוא דאיבעי ליה למיתנא דאפילו בתוך זמנו מותר בהנאה, ואיידי דתנא דישראל לאחר זמנו ⁠— תנא נמי דגוי לאחר זמנו.

And by right it should have taught that even the eating of leavened bread belonging to a non-Jew is permitted after the conclusion of Passover, but since the tanna taught that it is forbidden to derive benefit from leavened bread belonging to a Jew after Passover, he also taught that it is permitted to derive benefit from leavened bread belonging to a non-Jew. However, one should understand that it is permitted to eat this leavened bread as well. And similarly, by right it should have taught that even during Passover it is permitted to derive benefit from leavened bread that belongs to non-Jews. But since the tanna taught about the leavened bread belonging to a Jew after Passover, he also taught about the leavened bread belonging to a non-Jew after Passover. Thus, one should not infer halakhot from the exact formulation of these details in the baraita, but rather understand that the Mishnah follows R' Yehuda’s opinion.