Talmud - Eruvin 86b עירובין פ״ו ב׳

A cross beam of four handbreadths laid across a cistern located between two courtyards permits one to draw water from that cistern.

With this in mind, the following difficulty arises: The bucket he uses to draw the water might drift under the cross beam to the other side of the cistern and bring water from the other courtyard. The Gemara answers: The Sages have established that a bucket does not drift more than four handbreadths from the point where it was lowered, and it will therefore stay on its original side of the partition.

The Gemara raises a difficulty: Nonetheless, the water becomes intermingled under the cross beam, and consequently the bucket will bring up water from the other courtyard. Rather, it must be that the reason for the leniency is not that the cross beam actually prevents the flow of the water, but because the Sages were lenient with regard to water. They allowed a partition suspended above the water to be considered as though it blocked the flow of the water. As Rav Tavla asked of Rav: With regard to a suspended partition, does it permit carrying in a ruin? Do we say that the remnants of the walls suspended in the air are considered as though they descended to the ground and closed off the area, thereby rendering it a private domain? Rav said to him: A suspended partition of this kind permits carrying only in the case of water, as the Sages were lenient with regard to water.

The mishna teaches: Rabbi Yehuda said: There is no need for a partition in the cistern, as a partition inside a cistern is no better than the wall above it. Rabba bar bar Ḥana said that Rabbi Yoḥanan said: Rabbi Yehuda stated this in accordance with the opinion of Rabbi Yosei, who said: A suspended partition permits carrying even on land, as it is considered as though it descended to the ground and sealed off the area. Accordingly, there is no need to erect a partition inside the airspace of a cistern.

As we learned in a mishna: One who lowers sukka walls from above going downward, when the walls are three handbreadths higher than the ground, the sukka is invalid, as they are not considered partitions; but if he constructed walls from below going upward, if they are ten handbreadths high the sukka is valid, even if they do not reach the roofing.

Rabbi Yosei, however, says: Just as with regard to walls constructed from below going upward, ten handbreadths suffice, so too, in the case of walls built from above going downward, ten handbreadths are enough for it to be considered a whole wall, even if it more than three handbreadths above the ground. Similarly, Rabbi Yehuda maintains that a partition suspended above a cistern is considered as though it descended and sealed off the area.

The Gemara rejects this argument: But this is not so, for we can distinguish between the two opinions and claim that neither Rabbi Yehuda holds in accordance with Rabbi Yosei, nor does Rabbi Yosei hold in accordance with Rabbi Yehuda.

The Gemara elaborates: Rabbi Yehuda does not necessarily hold in accordance with Rabbi Yosei, as a distinction can be made between the two cases. Rabbi Yehuda stated his opinion only with regard to the joining of courtyards, which are required by rabbinic law, but in the case of a sukka, which is required by Torah law, no, he did not say that we can rely on suspended partitions.

And conversely, Rabbi Yosei does not necessarily hold in accordance with Rabbi Yehuda, as Rabbi Yosei stated his opinion only with regard to a sukka, which is a prohibition stated in the Torah from a positive commandment. The prohibition is not written as a negative commandment, but it can be inferred from a positive commandment. Neglect of the positive commandment of sukka is not punishable by the court, therefore we are not stringent in this regard. But with regard to Shabbat, which is a prohibition punishable by stoning, Rabbi Yosei did not state his opinion. Consequently, Rabbi Yosei might agree that we must be very stringent with regard to all halakhot of Shabbat, even those that are rabbinic in origin.

And if you ask: That incident, which occurred in Tzippori, when they relied on suspended partitions on land for Shabbat, on whose authority was it performed? It was done not on the authority of Rabbi Yosei, but rather it was performed on the authority of Rabbi Yishmael, son of Rabbi Yosei, who maintains that a suspended partition renders it permitted to carry even if it is over land and even on Shabbat.

The incident transpired in the following manner. As when Rav Dimi came from Eretz Yisrael to Babylonia, he said: It once happened that the people forgot and did not bring a Torah scroll to the synagogue on Friday while it was still day, which meant they were left without a scroll from which to read on Shabbat. On the following day, Shabbat, they spread a sheet over the pillars positioned between the house where the scroll was kept and the synagogue, thereby forming a corridor with partitions suspended on each side. And in this manner they brought the Torah scroll to the synagogue and read from it.

The Gemara expresses surprise at the wording of this account: Did they actually spread sheets on Shabbat? Is it permitted to do so ab initio? But doesn’t everyone agree that one may not erect a temporary tent on Shabbat ab initio? Spreading sheets over pillars is considered constructing a temporary tent.

Rather, what happened was that they found sheets spread over the pillars, which they used as partitions, and in this manner they brought the Torah scroll to the synagogue and read from it.

Rabba said: Rabbi Yehuda and Rabbi Ḥananya ben Akavya said the same thing. Both were very lenient with regard to the halakha of a partition over water. The ruling of Rabbi Yehuda is that which we just said, that the wall of the courtyard permits a cistern. The ruling of Rabbi Ḥananya ben Akavya is as we learned: Rabbi Ḥananya ben Akavya says: In the case of a balcony that contains four cubits by four cubits, which is suspended over water,

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Eruvin 86b examines using a suspended partition over a shared cistern and debates whether such partitions permit carrying on land as well as water.