Question: Yocheved was born when they entered the walls of Mitzrayim. This was at a time (during the second year) of famine.

You must say that they (Levi and his wife) had relations in famine years!

Answer: All agree that it is forbidden only to one who wants to conduct with Chasidus (beyond the letter of the law). Yosef did not have relations, but others did.

Question: We say in Bava Kama (91b) that one may wound himself, but others who wound him are liable;

Shmuel explains there that one may wound himself, i.e. he may fast.

Inference: Shmuel holds that one who fasts is not called a sinner!

Answer: Surely he is a sinner, like it says here, from a Kal va'Chomer from Nazir. A Nazir who pained himself only from wine [is called a sinner]...

In any case, the Mitzvah he does, i.e. fasting, is greater than the Aveirah of paining himself;

It is a Mitzvah to vow [to be a Nazir], like we say (Sotah 2a) "one who sees a Sotah in her disgrace should accept Nezirus from wine."

In any case, there is a small Aveirah, just like one who fasts on Shabbos due to an ominous dream;

The decree against him is torn, but he will be punished for fasting on Shabbos;

What is his solution [to avoid punishment]? He fasts to atone for fasting on Shabbos.

Explanation: [It is as if] ha'Kadosh Baruch Hu [is inside him, so he may not weaken Him];

[The Gemara questioned this, for] he said above that he is called Kadosh, i.e. one who fasts is called Kadosh. We answer that this is not difficult...

Explanation: He bestows Chesed to his Nefesh and does not fast. He is called a Chasid.

Explanation: They had much rain. (Therefore, they did not fast for rain.)

Question: Why does it discuss an individual? The same applies to a Tzibur!

We say in the Mishnah (10a) that we make three fasts, and one may eat [the night before] after dark. This requires investigation.

Explanation: He fasted during the day, and did not eat the next night, and spent the night in his fast.

Even though the [fast at] night was due to the fast he accepted on himself, he does not pray Tefilas Ta'anis (Aneinu)).

Bahag's opinion: There is a case of one who eats and pray Tefilas Ta'anis.

He explains that this is like here. In the morning he says Tefilas Ta'anis, even though he ate the entire night.

There is a case of one who fasts and does not pray [Tefilas Ta'anis], e.g. at night, even though he did not eat.

Explanation (Bahag): We do not say Tefilas Ta'anis in the morning, lest he be a liar in his Tefilah, for perhaps he will not complete the fast.

Rebuttal (Tosfos): He is not called a liar, for he intended to fast;

Even if Ones occurred afterwards and he cannot pain himself [and complete the fast], this is no worse than fasting hours!

Support: A Mishnah (Ta'anis 19a) says that if rain fell before midday, they do not complete [the fast]. It did not specify, so this connotes that they said Tefilas Ta'anis.

Disclaimer: This is not a full proof, for perhaps they did not say Tefilas Ta'anis.

Suggestion: We can bring a proof from the case of Rav Huna brei d'Rav Yehoshua brei d'Rav Idi (12b)!

He was fasting. They told him "borrow (do not complete the fast, so you can eat with us), and pay back (fast another day in place of it)." He said "I am fasting due to a dream."

Why didn't he say "[I must complete the fast] because I said Tefilas Ta'anis"?

Rejection: This is not a proof for Bahag. The day before, Rav Huna had not intended to fast (he fasted only due to a dream), so he did not accept it. (Therefore, he did not say Tefilas Ta'anis.)

Rabbeinu Meir's opinion: If the day before, one did not accept to fast, he does not say Anienu, unless he fasts due to a dream.

The custom: The custom is that the Shali'ach Tzibur says [Tefilas Ta'anis] in Shacharis, to inform everyone and mention the fast, but an individual does not say it until Minchah.

The Tur (OC 565) says the Shali'ach Tzibur says it every time, for surely at least some of the Tzibur are fasting.