Eiruvin 55b: Those who live in huts are as if they live in graves, and regarding their daughters it is written, “Cursed is he who lies with an animal.” Why? Because they notice when their neighbors go to the mikvah.

Hagahos Ashri, quoting Agudah: Based on this, women have the custom to be discreet on the night of their immersion, and are careful not to go in a noticeable manner.

Shulchan Aruch Yoreh Deah 198:48, Rema: Some have written that a woman must be discreet on the night of her immersion, and this is indeed the custom of women, to conceal the fact that they are going to the mikvah that night, not to go noticeably or in front of others, so that people should not notice. And whoever does not do so – regarding her it says, “Cursed is he who lies with an animal.”

עירובין נה ע”ב אליעזר איש ביריא אומר: יושבי צריפין כיושבי קברים, ועל בנותיהם הוא אומר (דברים כ״ז) ארור שכב עם כל בהמה. מאי טעמא? וכו’ רבי יוחנן אמר: מפני שמרגישין זה לזה בטבילה. וכתב בהגהות אשרי שם ד”ה יושבי כו’. ונ”ל בשביל זה נהגו הנשים להיות צנועות בליל טבילתן שלא לילך במהומה, אגודה.

רמ”א יו”ד קצ”ח סמ”ח יש שכתבו שיש לאשה להיות צנועה בליל טבילתה וכן נהגו הנשים להסתיר ליל טבילתן שלא לילך במהומה או בפני הבריות שלא ירגישו בהן בני אדם ומי שאינה עושה כן נאמר עליה ארור שוכב עם בהמה.

The holy Shamloyer Rav zt”l, Rabbi Shlomo Zalman Ehrenreich, who perished Al Kiddush Hashem in the Holocaust, was one of the greatest Torah scholars of his time. He published many volumes of chiddushim, had a reputation as a fiery speaker, and taught generations of students.

It once happened that the pipes of the mikvah in Shamloy burst, causing the walls of the building to cave in. The entire mikvah needed to be rebuilt. Since the old mikvah stood on a very low spot relative to the city, and was reachable only via a long staircase, the leaders of the kehillah decided to rebuild it in a better, more accessible place.

But the Shamloyer Rav did not agree, because the new location was to be in a crowded Jewish neighborhood where everyone would see the women coming and going from the mikvah. The Rema says (198:48) that a woman must go to the mikvah discreetly, unnoticed by others in the city. Therefore, the Rav wanted the mikvah rebuilt in its old location.

One of the board members of the kehillah was a building contractor, and he argued that it would be dangerous to rebuild the mikvah in its old location. The kehillah board members were in a dilemma. On the one hand, they wanted to follow their Rav, who assured them it could be built safely in the old location, but on the other hand they feared that the contractor might be correct.

And so the rebuilding project was delayed, which pained the Rav greatly. He wanted to see the mikvah rebuilt as soon as possible.

One Shabbos afternoon, as he was saying his Pirkei Avos shiur, he came to a mishnah in the first perek which begins with the words, “He used to say…” The Rav posed the question: Why does the mishnah have to say these words?  Why can’t it just proceed directly with the quotation? 

He answered this based on the Gemara in Sotah 5a, which says that a Torah scholar should have a small measure of pride – an eighth of an eighth. Why? Isn’t arrogance a bad character trait? The Vilna Gaon explains that the Gemara is alluding to the eighth posuk in the eighth parsha of the Torah, in which Yaakov Avinu says, “I have become smaller due to all the kindness and truth You have shown Your servant.” Yaakov Avinu was implying that he did indeed have past merits, but Hashem had already rewarded him for them. 

Usually, the Shamloyer Rav continued, a person reaches humility by comparing himself with others who are greater than him. But talmidei chachomim and tzaddikim can reach humility in a different way: by comparing their current selves to their old selves. They should recall with pride their younger years, when they used to learn so diligently and daven with kavanah, but then think, “Today I’m older and weaker; I’m not as great as I once was.”

And that brings us to the explanation of our mishnah: “He used to say.” Just as Yaakov Avinu believed he had some merits from his younger years, our Tanna, with an eighth of an eighth of pride, said that in the old days he used to say good Torah.

At this point the Shamloyer Rav raised his voice and began to speak in the fiery style for which he was so famous: “I can testify that once upon a time, I was a true yerei shomayim. I learned Torah day and night.   On many nights, I stayed up learning Torah all night long. Without a doubt, I have some reward awaiting me in Olam Haba.  Everyone knows that the reward for learning Torah is tremendous. For the little that I learn nowadays, I don’t think I will deserve any reward. But in the old days when I was young, I learned with all my strength and for that I deserve some reward.

“And I announce here publicly that I give up my entire reward to anyone who can pay to rebuild the mikvah in its old location, as I want it, so that it should be a place of privacy and tznius!”

The audience was shocked to hear these intense words, spoken in all seriousness, coming out of his holy mouth. The next morning, Mr. Avraham Lauber came to the Rav and said, “I take you up on your offer. I am ready to pay for the entire mikvah in exchange for the Rav’s reward in Olam Haba.”

The Rav’s face shone with happiness. With tears running down his cheeks, he shook hands with Mr. Lauber, and said to him clearly: “I hereby give you my share in Olam Haba, my reward for the Torah that I learned in my young years, as a complete and irreversible gift.”

With the money donated, the Rav hired a new contractor from Grossvardein, who was able to build the mikvah in its old location.

Source: Even Shleimah, v. 1, Toldos Rabbeinu