Pesachim, Chapter 9, Mishnah 5. The Mishnah sets out to clarify: what is the difference between the Pesach of Egypt and the Pesach of later generations? What distinctions were there between the Pesach offering that Israel brought while still in Egypt and the Pesach offering brought throughout the generations?
The differences listed by the Mishnah:
"Pesach Mitzrayim mikacho mibe'asor" - in Egypt, Israel were commanded to set aside the Pesach offering already from the tenth of Nissan. In later generations there is indeed an obligation to inspect the animal for any blemish or defect over a period of four days, so that it must be examined from the tenth onward, but there is no need to actually designate it as an offering already from the tenth, as was done in Egypt. One may examine any animal, and if it is found to be unblemished over the course of four days, it is fit to serve as a Pesach offering. That is the difference.
"Ve'ta'un haza'as hadam ba'agudas ezov al hamashkof ve'al shtei hamezuzos" - this sprinkling, with a bundle of hyssop branches, applied only to the Pesach of Egypt, and we are not obligated in it; on the contrary, in later generations the blood is placed on the altar.
"Vene'echal bechipazon" - the Pesach offering in Egypt had to be eaten quickly and in haste.
"Ulaylah echad" - this seems difficult, for the Pesach of later generations is likewise eaten for one night only. The Gemara explains that words are missing from the wording of the Mishnah, and its essential intent is: "Vechimutzo noheg yom echad" - the prohibition of chametz in Egypt applied for one day only, the fifteenth of Nissan, "uPesach doros noheg kol shivah" - whereas in later generations the prohibition of chametz applies all seven days of Pesach.
In summary: this Mishnah lists the differences between the Pesach of Egypt and the Pesach of later generations: taking the offering from the tenth of the month, sprinkling the blood with a bundle of hyssop on the lintel and the two doorposts, eating it in haste, and the prohibition of chametz that applied for one day only, as opposed to the Pesach of later generations, in which the prohibition of chametz applies for all seven days.