Berachos, Chapter 6, Mishnah 8. This mishnah deals with two questions: over which foods do we recite Birkas HaMazon, and what is the proper berachah for someone who drinks water to quench his thirst.
The View of Rabban Gamliel:
Someone who ate figs, grapes or pomegranates - according to Rabban Gamliel "mevarech achareihen shalosh berachos" - he recites three berachos afterward, meaning the complete Birkas HaMazon.
Why does the mishnah use the expression "three berachos"?
Because from the Torah, Birkas HaMazon consists only of the first three berachos. The berachah of "HaTov VehaMeitiv" was instituted at a later period; it is not from the Torah and is not counted among the essential berachos. For this reason Rabban Gamliel refers to Birkas HaMazon as "three berachos."
Rabban Gamliel's Reasoning:
Why does Rabban Gamliel hold that one must recite Birkas HaMazon even after eating these fruits? The verse from which the obligation to bless is derived - "ve'achalta vesavata uveirachta es Hashem" - "you shall eat and be satisfied and bless Hashem" - comes immediately after the passage listing the seven species with which the Land of Israel is praised. Rabban Gamliel therefore understands that the obligation to bless after eating applies to everything listed in that passage: wheat, barley, grapes, figs and pomegranates - all of them are included in the obligation.
The Halachah:
We do not rule according to this view. Over these fruits - figs, grapes and pomegranates - we recite the berachah of 'Al HaPeiros.' Just as over foods made from grain we recite 'Al HaMichyah,' so too after eating one of the seven species we recite 'Al HaPeiros.'
One Who Drinks Water to Quench His Thirst:
From here the mishnah moves to a discussion of the proper berachah for drinking water:
One who drinks not to quench his thirst - such as someone swallowing a pill or trying to clear his throat - does not recite a berachah at all.
One who drinks to quench his thirst - recites "shehakol nihyah bidvaro" - that everything was created by His word.
The View of Rabbi Tarfon:
Rabbi Tarfon disagrees and holds that one does not recite "shehakol," but rather "borei nefashos rabbos vechesronan" - the berachah we are accustomed to reciting after eating. In his opinion, this is the berachah recited before drinking water.
Here too the halachah does not follow his words. The berachah of 'Borei Nefashos Rabbos' is a berachah recited after eating, in cases where there is no obligation of 'Al HaMichyah,' 'Al HaGefen' or 'Al HaPeiros,' and it is not said beforehand; before drinking water we recite "shehakol nihyah bidvaro."
In summary: In this mishnah we learned the view of Rabban Gamliel, that one who eats figs, grapes or pomegranates recites three berachos afterward - the complete Birkas HaMazon - since the verse "ve'achalta vesavata uveirachta" appears immediately after the passage of the seven species; and the halachah is that over these fruits we recite the berachah of 'Al HaPeiros.' We also learned the dispute between Rabban Gamliel and Rabbi Tarfon concerning the berachah of one who drinks water to quench his thirst - "shehakol nihyah bidvaro" or "borei nefashos rabbos" - and the halachah is that we recite "shehakol" before drinking, and 'Borei Nefashos Rabbos' afterward.