Sanhedrin 68A

והא רבי עקיבא מרבי יהושע גמיר לה? והתניא: כשחלה רבי אליעזר, נכנסו רבי עקיבא וחביריו לבקרו. הוא יושב בקינוף שלו, והן יושבין בטרקלין שלו.

The Talmud asks: And did R' Akiva learn these halakhot from R' Yehoshua? But isn’t it taught in a baraita: When R' Eliezer took ill, R' Akiva and his colleagues came to visit him. He was sitting on his canopied bed [bekinof ], and they were sitting in his parlor [biteraklin]; they did not know if he would be able to receive them, due to his illness.

ואותו היום ערב שבת היה, ונכנס הורקנוס בנו לחלוץ תפליו. גער בו ויצא בנזיפה. אמר להן לחביריו: כמדומה אני שדעתו של אבא נטרפה. אמר להן: דעתו ודעת אמו נטרפה! היאך מניחין איסור סקילה ועוסקין באיסור שבות?

And that day was Friday, and R' Eliezer’s son Hyrcanus entered to remove his tefillin, as tefillin are not worn on Shabbat. His father berated him, and he left reprimanded. Hyrcanus said to his father’s colleagues: It appears to me that father went insane, since he berated me for no reason. R' Eliezer heard this and said to them: He, Hyrcanus, and his mother went insane. How can they neglect Shabbat preparations with regard to prohibitions punishable by stoning, such as lighting the candles and preparing hot food, and engage in preparations concerning prohibitions by rabbinic decree, such as wearing tefillin on Shabbat?

כיון שראו חכמים שדעתו מיושבת עליו, נכנסו וישבו לפניו מרחוק ארבע אמות.

Since the rabbis perceived from this retort that his mind was stable, they entered and sat before him at a distance of 4 cubits, as he was ostracized (see Bava Metzia 59b). It is forbidden to sit within 4 cubits of an ostracized person.

אמר להם: למה באתם? אמרו לו: ללמוד תורה באנו. אמר להם: ועד עכשיו למה לא באתם? אמרו לו: לא היה לנו פנאי. אמר להן: תמיה אני אם ימותו מיתת עצמן. אמר לו רבי עקיבא: שלי מהו? אמר לו: שלך קשה משלהן.

R' Eliezer said to them: Why have you come? They said to him: We have come to study Torah, as they did not want to say that they came to visit him due to his illness. R' Eliezer said to them: And why have you not come until now? They said to him: We did not have spare time. R' Eliezer said to them: I would be surprised if these rabbis die their own death, i.e., a natural death. Rather, they will be tortured to death by the Romans. R' Akiva said to him: How will my death come about? R' Eliezer said to him: Your death will be worse than theirs, as you were my primary student and you did not come to study.