Berachos, Chapter 1, Mishnah 5. This is probably the best known Mishnah in all of Shas, and the reason is simple: the entire Mishnah, word for word, is woven into the text of the Haggadah that we read on Seder night.
"Mazkirin yetzias Mitzrayim ba'leilos" - We mention the Exodus from Egypt at night:
The Mishnah opens by establishing that mentioning the Exodus from Egypt is not limited to the daytime, but is said at night as well. This mention is made by reciting the passage of tzitzis. The need for this ruling arises from the wording of the verse, which commands us to remember the Exodus "all the days of your life" - wording that could be understood as referring to the days alone, as will be explained further on in the Mishnah.
"Amar Rabbi Elazar ben Azaryah: harei ani ke'ven shivim shanah" - Rabbi Elazar ben Azaryah said: I am like a man of seventy years:
Rabbi Elazar ben Azaryah opens by declaring that he is "like a man of seventy years." This refers to the famous incident recorded in the Gemara: he was only about eighteen years old when he was appointed head of the Sanhedrin, and at the time of his appointment Heaven gave him white hairs in his beard, so that he appeared to be seventy years old, even though he was in fact exceedingly young.
He continues: "velo zachisi she'tei'amer yetzias Mitzrayim ba'leilos, ad she'derashah ben Zoma" - and I did not merit that the Exodus from Egypt be mentioned at night until ben Zoma expounded it. That is, he did not succeed in prevailing over those who disagreed with him and establishing that the Exodus be mentioned at night, until ben Zoma came and expounded the verse: "lema'an tizkor es yom tzeischa me'eretz Mitzrayim kol yemei chayecha" - so that you remember the day you went out of the land of Egypt all the days of your life.
There are two ways of explaining the verse:
Ben Zoma's derashah: "yemei chayecha" (the days of your life) - from the word "yemei" (days) alone, the days are obligated; "kol yemei chayecha" (all the days of your life) - the word "kol" (all) comes to include the nights as well.
The derashah of the Chachamim: The Chachamim rejected this exposition and expounded differently - "yemei chayecha" refers to this world, and even here we are still speaking of the days alone; while "kol yemei chayecha" does not come to include the nights, but rather "lehavi limos haMashiach" - to include the days after the coming of Mashiach.
According to the derashah of the Chachamim, even after we experience, with Hashem's help, miracles far greater than those of the Exodus from Egypt, the Exodus will remain something that we know and remember on a daily basis.
To summarize: In this Mishnah we learned that the Exodus from Egypt is mentioned at night as well, and that this is derived from ben Zoma's exposition of the verse "lema'an tizkor es yom tzeischa me'eretz Mitzrayim kol yemei chayecha," since the additional word "kol" comes to include the nights. We also learned the derashah of the Chachamim who disagree, who hold that "kol yemei chayecha" comes to include the days of Mashiach, teaching us that even in the future the remembrance of the Exodus from Egypt will be preserved as an everyday matter.