Rif Brachot 40b

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40b

{Brachot 53b continued}
כִּי אֲנִי ה, אֱלֹקֵיכֶם - 'For I am the LORD your God' {from the beginning of the verse} - this the is blessing. {Rashi: at the end of the meal, Birchat HaMazon; Rabenu Yona: upon washing your hands.}

We learn in perek kol haBasar {Chullin, 8th perek, daf 105a}: Rav Iddi bar Avin cited Rav Yitzcahk bar Asiyan: First water is a mitzvah {~commandment}; final water is a chova {obligation}.
They posed a contradiction: first and final waters are a chova; middle waters are a reshut {voluntary}.
{The answer:} A mitzvah is called a chovah compared with a reshut.

Gufa {return to discuss the subject mentioned above}:
first and final waters are a chova; middle waters are a reshut; first waters are taken {we wash with them} whether in a vessel or upon the ground; final {waters} are only taken in a vessel, and others say "are not taken upon the ground." This is the difference between them {the two wordings}: kinsa - to explain, this refers to small planks of wood. The first ones are taken whether hot or cold; final - only cold, but hot, no, because hot water softens the hands but does not remove the grease. And this only refers to water so hot that it scalds the hands, but lukewarm water, we have no problem with it.

"The middle waters are voluntary"
Rav Nachman said: They only said this {that it was voluntary} between a tavshil {cooked dish} to another tavshil {cooked dish}, but between a tavshil to cheese, no.
{See Rabenu Yona, and see the gemara and the Tosafot there, for the meaning of this statement.}

Rav Yehuda bar Rav Chiyya said: Why did they say that final water is a chova? For one eats after his meal salt, and there is in it salt of Sodom {a very fine salt}, which blinds the eyes.
Abaye said: and we {only} find it in the amount of a korta in a kur.

And if you measure salt you need to wash your hands.

{Chullin 106a}
Water heated in a flame, Chizkiya said: we use to wash hands, and Rabbi Yochanan said: we do use for washing hands.

And Rabbi Yochanan said: I asked Rabban Gamliel son of Rabbi: may he eat taharot {with such a washing}, and he said to me: all the great men of Galil did so.

And we establish like Rabbi Yochanan in this.

The waters of Teveria {hot water springs}, Chizkiya said: we do not wash hands with them, and Rabbi Yochanan said: his entire body he may immerse in them - his hands (and feet) should certainly be so.
Rav Pappa said: In their place {attached to the main body of water, and he is immersing his hands}, all agree that it is permitted; to wash with it in a vessel (not in their place), all agree that it is forbidden. When do they argue? Where you separated it in a small ditch {Rashi: and there is not in the ditch itself the shiur but it is connected to the rest of the water, and it is simply a decree in consideration of the case of a vessel}. Chizkiya said we make a decree for a small ditch in consideration of the case of a vessel, and Rabbi Yochanan holds we do not make a decree.

And the halacha is like Chizkiya, for he is the teacher of Rabbi Yochanan.

And if you ask from the halacha above {where we ruled that heated water was acceptable}, there they had a time