...The Sages taught: Four entered the Paradise, i.e., dealt with the loftiest secrets of Torah, and they are as follows: Ben Azzai; and ben Zoma; Aḥer, the other, a name for Elisha ben Avuya; and Rabbi Akiva. Rabbi Akiva, the senior among them, said to them: When, upon your arrival in the upper worlds, you reach pure marble stones, do not say: Water, water, although they appear to be water, because it is stated: “He who speaks falsehood shall not be established before My eyes” (Psalms 101:7).
>https://www.sefaria.org/Chagigah.14b.8?lang=bi
The Gemara proceeds to relate what happened to each of them: Ben Azzai glimpsed at the Divine Presence and died. And with regard to him the verse states: “Precious in the eyes of the Lord is the death of His pious ones” (Psalms 116:15). Ben Zoma glimpsed at the Divine Presence and was harmed, i.e., he lost his mind. And with regard to him the verse states: “Have you found honey? Eat as much as is sufficient for you, lest you become full from it and vomit it” (Proverbs 25:16). Aḥer chopped down the shoots of saplings. In other words, he became a heretic. Rabbi Akiva came out safely.
>https://www.sefaria.org/Chagigah.14b.9?lang=bi