Beitzah, Chapter 3, Mishnah 8. The Mishnah opens: "Omer adam la'chaveiro malei li kli zeh" - a person may say to his fellow, "Fill this vessel for me."
"Malei li kli zeh, aval lo b'midah": - "Fill this vessel for me," but not by measure:
The Mishnah is speaking about a shopkeeper who distributes merchandise, primarily liquid merchandise, into the vessels of his customers. That was the practice: people would bring their own vessels, and the shopkeeper would fill them. The Mishnah teaches that a person may say to the shopkeeper on Yom Tov, "Fill this vessel for me" - fill it with wine or with oil.
According to the Gemara, this is permitted even though the vessel itself is a measuring vessel, that is, a vessel of a fixed measure. There is only one condition - "aval lo b'midah" - but not by measure: as long as the buyer does not mention the measure itself, such as saying, "Fill this log for me." He says only, "Fill this vessel," and does not say, "Measure out for me."
The reason: we do not measure on Yom Tov except for the purpose of a mitzvah, since measuring was the manner of buying and selling, and one must distance himself from anything that recalls or resembles the way of commerce. Therefore one does not mention a measure and does not state its amount, but says only, "Fill this vessel."
The view of Rabbi Yehudah:
Rabbi Yehudah is stringent and says: "Im kein, kli she'hu shel midah - lo yemalenu" - if so, a vessel that is a measuring vessel may not be filled. Even if the buyer does not mention the name of the measure, the very fact that the vessel is designated for measuring prevents its use on Yom Tov for receiving merchandise from the shopkeeper.
The incident with Abba Shaul ben Batnis:
The Mishnah brings an incident: "Ma'aseh b'Abba Shaul ben Batnis she'hayah memalei midosav me'erev Yom Tov v'nosein la'lakochos b'Yom Tov" - there was an incident with Abba Shaul ben Batnis, who would fill his measures on the eve of Yom Tov and give them to his customers on Yom Tov. He would fill the measures and the customers' vessels with oil and wine already before Yom Tov, and hand them over on Yom Tov itself - because he held like Rabbi Yehudah, that one may not fill vessels that are themselves measures.
"Af ba'moed oseh kein, mipnei bi'ur ha'midos": - he did the same on Chol HaMoed as well, because of the clearing out of the measures:
Abba Shaul said that on Chol HaMoed too he would act this way. On Chol HaMoed there is no problem with measuring at all, and measuring is permitted; rather, he filled the vessels in advance in order to make sure that the measures were properly full. The reason: on Chol HaMoed many people would come to him to learn Torah, since they were not engaged in their regular work and were free to study. As a result he was busier than usual, and he did not have the time to verify that his customers' measures were properly full, without residue or foam at the top of the vessel. He therefore did this the night before.
And the Sages said that even on ordinary weekdays, and not only on Chol HaMoed, he would act this way - "mipnei mitzui ha'midos" - because of the draining of the measures. "Draining" means squeezing out the liquid to the very last drop: that all the oil or wine should come out of the shopkeeper's vessel and enter the buyer's vessel, so that the buyer receives the full amount he paid for and nothing remains in the seller's vessel. This reflects an extra measure of honesty and care in giving the buyer the full purchase.
Counting eggs and nuts on Yom Tov:
The Mishnah continues with a further halachah regarding Yom Tov: a person may go to the shopkeeper he regularly patronizes and say to him, give me eggs or nuts by number, that is, he may state a number - ten eggs or fifty nuts. The reason: with items of this kind, such counting is the way householders count within their own homes. Therefore it does not recall buying and selling or the manner of conducting business, but rather something people do in their homes, and so it is permitted even on Yom Tov.
In summary: in this Mishnah we learned that one may say to a shopkeeper on Yom Tov, "Fill this vessel for me," provided that he does not mention a measure, since we do not measure on Yom Tov except for the purpose of a mitzvah, because measuring resembles the way of commerce. Rabbi Yehudah is stringent and forbids even filling a vessel that is a measuring vessel. We brought the incident with Abba Shaul ben Batnis, who filled his measures on the eve of Yom Tov and gave them to his customers on Yom Tov, and the reasons for filling them in advance - "clearing out the measures" on Chol HaMoed, because he was busy learning with the many people who came to him, and "draining the measures" even on weekdays, so that the buyer would receive his full purchase. Finally we learned that one may request eggs and nuts by number, since this is the way of a householder within his home and involves nothing of buying and selling.