Pesachim 28B

רבי שמעון אומר: חמץ לפני זמנו ולאחר זמנו ⁠— אינו עובר עליו בלא כלום. תוך זמנו ⁠— עובר עליו בכרת ובלאו. ומשעה שאסור באכילה אסור בהנאה, אתאן לתנא קמא. רבי יוסי הגלילי אומר: תמה על עצמך, היאך חמץ אסור בהנאה כל שבעה!

R' Shimon says: One who eats or derives benefit from leavened bread, both before its time and after its time, does not transgress any prohibition. During its time one is liable to receive karet and transgresses a negative mitzva for eating or deriving benefit from leavened bread. And from the time that it is prohibited to eat leavened bread, beginning at midday on Passover eve, it is also prohibited to derive benefit from it. The Talmud comments: With this last sentence we have come to the opinion of the first tanna, as this statement appears to present R' Yehuda’s opinion and not that of R' Shimon. R' Yosei HaGelili says: Be astounded with yourself. How can it be prohibited to derive benefit from leavened bread for all 7 days? In other words, he disagrees with the premise that it is prohibited to derive benefit from leavened bread even during the 7 days of Passover.

ומנין לאוכל חמץ משש שעות ולמעלה שהוא עובר בלא תעשה ⁠— שנאמר: ״לא תאכל עליו חמץ״, דברי רבי יהודה.

The baraita discusses a related issue: From where is it derived that one who eats leavened bread on Passover eve from the 6th hour and onward transgresses a negative mitzva? As it is stated: “And you should sacrifice the Paschal lamb to YHWH your God, of the flock and the herd, in the place which YHWH should choose to cause His name to reside there. You should eat no leavened bread with it; for 7 days you should eat matzot, the bread of affliction” (Deuteronomy 16:2–3). The juxtaposition of the Paschal lamb with the prohibition of leavened bread teaches that the prohibition to eat leavened bread begins from the time that the Paschal lamb is slaughtered, namely, the afternoon of the 14th of Nisan. This is the statement of R' Yehuda.