Mishnà su Genesi 40:26

In three cases Rabban Gamaliel was strict like the words of Beth Shammai.One may not wrap up hot food on a festival for the Sabbath; And one may not join together a lamp on a festival; And one may not bake [on festivals] thick loaves but only wafer-cakes. Rabban Gamaliel said: “In all their days, my father’s house never baked large loaves but only wafer-cakes.” They said to him: “What can we do with regards to your father’s house, for they were strict in respect to themselves but were lenient towards Israel to let them bake both large loaves and even charcoal-roasted loaves.”