Reference for Shabbat 147:2

ת"ר היו לפניו מיני אוכלין בורר ואוכל בורר ומניח ולא יברור ואם בירר חייב חטאת מאי קאמר אמר עולא הכי קאמר בורר ואוכל לבו ביום ובורר ומניח לבו ביום ולמחר לא יברור ואם בירר חייב חטאת מתקיף לה רב חסדא וכי מותר לאפות לבו ביום וכי מותר לבשל לבו ביום

Raba said: This agrees with Rabbi, who said: The primary labours are forty less one; but if pounding were enumerated, there would be forty.<span class="x" onmousemove="('comment',' Rabbi deduces even the number of labours from Scripture (v. infra 97b). ');">⁴</span> Then let one of these be omitted and pounding be inserted? Hence it is clear [that it must be explained] as Abaye [does]. Our Rabbis taught: If various kinds of food lie before one, he may select and eat, select and put aside; but he must not select, and if he does, he incurs a sin-offering. What does this mean? — Said 'Ulla, This is its meaning: He may select to eat on the same day, and he may select and put aside for the same day; but he must not select for [use on] the morrow, and if he does, he incurs a sin-offering. R. Hisda demurred: Is it then permitted to bake for [use on] the same day, or is it permitted to cook for the same day?<span class="x" onmousemove="('comment',' Surely not! And since you say that selecting for use on the next day entails a sin-offering, it is a forbidden labour in the full sense of the term, and hence prohibited even if required for the same day. ');">⁵</span>

Explore reference for Shabbat 147:2. In-depth commentary and analysis from classical Jewish sources.