Pesachim 109B

אמה על אמה ברום שלש אמות, ושיערו חכמים שיעור מי מקוה ארבעים סאה.

A cubit, by a cubit, by a height of 3 cubits. And the rabbis measured the measure of the water necessary for a mikveh at 40 se’a.

אמר רב אשי: אמר לי רבין בר חיננא, שולחן של מקדש ⁠— של פרקים הוה, דאי סלקא דעתך הדוקי הוה מיהדק, אמתא באמתא היכי מטבליה?!

The Talmud cites a discussion related to the topic of measurements. Rav Ashi said: Ravin bar Ḥinnana said to me: The table of the Temple, upon which the showbread was placed, was comprised of assembled parts. For if it should enter your mind that the table was firmly connected and could not be taken apart, how could the priests immerse a cubit in a cubit? The dimensions of the table were two cubits by 1 cubit, with a height of 1½ cubits. If the table contracted ritual impurity, it had to be immersed in a mikveh. If a mikveh contains an area of 1 cubit by 1 cubit, the table can fit inside only if it is dismantled.

מאי קושיא? דילמא בים שעשה שלמה הוה מטביל ליה. דתני רבי חייא: ים שעשה שלמה מחזיק מאה וחמשים מקוה טהרה.

The Talmud responds: What is the difficulty? Perhaps the priest would immerse it in the sea that King Solomon built, which was a very wide mikveh, as it states: “And he made the molten sea of 10 cubits from brim to brim, round in compass” (I Kings 7:23). As R' Ḥiyya taught: The sea that Solomon built contained the volume of water of 150 ritual purification baths. It was certainly possible to immerse even large vessels in this sea.

ולא יפחתו לו מארבעה. היכי מתקני רבנן מידי דאתי בה לידי סכנה, והתניא: לא יאכל אדם תרי, ולא ישתה תרי, ולא יקנח תרי, ולא יעשה צרכיו תרי?

We learned in the Mishnah that even with regard to the poorest of Jews, the charity distributors should not give him less than 4 cups of wine. The Talmud asks: How could the rabbis establish a matter through which one will come to expose himself to danger? But wasn’t it taught in a baraita: A person should not eat pairs, i.e., an even number of food items; and he should not drink pairs of cups; and he should not wipe himself with pairs; and he should not attend to his sexual needs in pairs. The concern was that one who uses pairs exposes himself to sorcery or demons. Why would the rabbis require one to drink an even number of cups and thereby place himself in a position of danger?