משנה על ביצה 3:16

The following cases are [examples] of the lenient rulings of Beth Shammai and of the rigorous rulings of Beth Hillel.An egg which is laid on a festival Beth Shammai says: it may be eaten, and Beth Hillel says: it may not be eaten. Beth Shammai says: yeast as much as an olive [in quantity], and leavened food as much as a date, and Beth Hillel says: as much as an olive [in quantity] in both cases.