Beitzah 29B

שמואל ⁠— הלכה למעשה אתא לאשמועינן.

it is reasonable to conclude that Shmuel came to teach us the practical halakha. Knowing that a baraita permits the practice, Shmuel found it necessary to state that the halakha is otherwise.

תנו רבנן: אין שונין קמח ביום טוב. משום רבי פפייס ורבי יהודה בן בתירא אמרו: שונין. ושוין שאם נפל לתוכן צרור או קיסם, ששונין.

§ A baraita states: One may not sift flour a second time on a Festival, as this involves unnecessary extra effort. They said in the name of R' Papeyyas and R' Yehuda ben Beteira: One may sift flour a second time. However, they all agree that if a pebble or a wood chip fell into the flour after it had been sifted the previous day, one may sift it a second time in order to remove the items.

תני תנא קמיה דרבינא: אין שונין קמח ביום טוב, אבל נפל צרור או קיסם ⁠— בורר בידו. אמר ליה: כל שכן דאסור, דהוה ליה כבורר.

A tanna taught the following baraita before Ravina: One may not sift flour a second time on a Festival, but if a pebble or a wood chip fell into the flour after the first sifting, he may remove it with his hand. Ravina said to him: All the more so is the latter procedure prohibited, as it is similar to the prohibited labor of selecting. It is therefore preferable to sift the flour with a sieve, and the unwanted items will thereby be removed.

דרש רבא בר רב הונא זוטי אפתחא דנהרדעא: שונין קמח ביום טוב. אמר להו רב נחמן: פוקו ואמרו ליה לאבא: שקילא טיבותך ושדי[א] אחזרי, פוק חזי כמה מהולתא הדרן בנהרדעא.

Rava bar Rav Huna the Short taught at the entrance to Neharde’a: One may sift flour a second time on a Festival. Rav Naḥman said to the students standing before him: Go out and say to Abba, i.e., to Rava bar Rav Huna, as Rava is a shortened form of Rav Abba: Your good has been removed and cast upon thorns, meaning that your teachings are not needed. Go out and see how many sieves circulate in Neharde’a, as all the women already know that this is permitted.