Gemara

(Beraisa - R. Oshaya): "He will grow Pera" means at least 30 days growth of hair;

Rebbi Yonason says, we need not learn from there. It says "Ad (until) completion of the days." Days that require completion are (of a full month, i.e.) 30.

Suggestion: Rav Masna (who says that Stam Nezirus is 30 days) holds like R. Oshaya. Bar Pada (who say that it is 29) holds like Rebbi Yonason (Nezirus is Ad (until) 30 days, but not Ad Bichlal, i.e. the final day (30) is not included).

Rejection: Both Tana'im hold like Rav Masna. R. Oshaya expounds "Ad'", but not Ad Bichlal. (Therefore, he needs to learn 30 from "Kodesh Yihyeh".) R. Yonason expounds "Ad", and Ad Bichlal.

Menachos 68a (Mishnah): After the Churban, R. Yochanan ben Zakai enacted to forbid Chodosh (this year's grain, which is forbidden until offering the Omer on Nisan 16) the entire day of the 16th.

R. Yehudah: It is forbidden mid'Oraisa - "Ad Etzem ha'Yom ha'Zeh"!

68b (Rav Nachman bar Yitzchak): R. Yochanan ben Zakai holds like R. Yehudah, who expounds "Ad Etzem ha'Yom ha'Zeh" - (after the Churban, it is forbidden) until the day. R. Yehudah holds Ad v'Ad Bichlal (also the day itself is forbidden.)

Question: R. Yehudah argues with R. Yochanan ben Zakai in the Mishnah!

Answer: R. Yehudah mistakenly thought that R. Yochanan ben Zakai forbids mid'Rabanan. Really, also R. Yochanan forbids mid'Oraisa. He did not enact to forbid the day, rather, he expounded and taught this to people.

Ravina's father would not eat Chodosh until the night after the 17th. He holds like R. Yehudah, and he is stringent about the doubt of the day (in Chutz la'Aretz).

Nedarim 61b (Mishnah): If one vowed 'until the harvest', he is forbidden only until it begins. The rule is, if something has a fixed time, if he said 'until it comes', he is forbidden until the start. If he said 'until it will be', he is forbidden until the end. If something has no fixed time, in either case he is forbidden only until the start.

Chulin 54b (Rav Nachman): Our Mishnah teaches that a hole in the windpipe 'Ad the size of an Isar' is Kosher. Exactly an Isar is like more than an Isar.

Inference: 'Ad' means Ad v'Lo Ad Bichlal.

55a - Question (Beraisa): A Log is like less than a Log. A Se'ah is like less than a Se'ah. Two Sa'im is like less than two Sa'im.

Retraction: Rather, we always explain 'Ad' in the more stringent way.

Rishonim

Rif and Rosh (Pesachim 28a and 10:42): Ravina's father would not eat Chodosh until the night after the 17th. He holds like R. Yehudah, and he is stringent about the doubt of the day.

Rambam (Hilchos Ma'achalos Asuros 10:2): When there is no Mikdash, Chodosh is forbidden the entire day of the 16th. In places that observe two days of Yom Tov, it is forbidden the entire day of the 17th, until evening.

Question (Or Some'ach 10:4): Why did R. Yochanan ben Zakai enact to forbid the entire day of the 17th? The concern lest (when the Mikdash is rebuilt) people forget an explicit verse is remote. His enactment may lead people to think that Ad v'Ad Bichlal, and they will permit grain that took root during the day of the 16th, which is really Chodosh (for really, dawn permits)!

Poskim

Shulchan Aruch (489:10): Even nowadays, one may not eat Chodosh bread, parched or rolled grain until the beginning of the night of the 18th, and in Eretz Yisrael, until the beginning of the night of the 17th.

Shulchan Aruch (CM 43:27): If Reuven has a document against Shimon dated Nisan 5, and Shimon has a receipt in which Reuven pardoned all claims against Shimon Ad Nisan 5, Reuven collects. The way people speak, Ad is Lo Ad Bichlal.

Source: Teshuvas ha'Rosh (76:4, cited in Beis Yosef DH v'Chosav Od): For Isur, we say Ad v'Ad Bichlal or v'Lo Ad Bichlal, whichever is more stringent. Nedarim follow the way people speak, i.e. v'Lo Ad Bichlal (Nedarim 61b).

Beis Yosef (ibid.): The Rosh (76:3) says that if a receipt says that David pardoned all claims against Levi Ad today, and David has a document against Levi with the same date, and says that he pardoned other claims, David has the lower hand. The Rashba (3:9) agrees. It is rare to pardon a debt right after lending, but circumstances can change suddenly. We are concerned lest a loan was paid the day it was given (Bava Metzia 17a)!

Question (Darchei Moshe 6): The Rosh contradicts what he wrote in 76:4!

Answer #1 (Hagahos Drishah 8): The Beis Yosef brings both Teshuvos, and did not ask this. If the receipt has a date at the beginning, and later it says that he pardoned all debts until that day, the repetition shows that he does not include that day. Alternatively, in Teshuvah 3, the document does not say 'until this day.' The Rosh says that (we know that) he pardoned until that day from the date. The Beis Yosef said that the Rashba agrees; the Rashba does not say that the document said 'until this day.'

Shach (45): If it were a contradiction, we would follow Teshuvah 4, for the Gemara always treats documents like Nedarim; we follow the way people speak. A vow 'Ad Pesach' does not include Pesach (YD 220:12). The Rema did not comment here, for he later agreed that there is no contradiction.

Answer #2 (Mahara Sason 80, brought in Shach): In Teshuvah 3, David admits that his pardon included today, but he says that the receipt preceded the loan. Levi disagrees. We don't make him pay due to a Safek. In Teshuvah 4, David says that he did not pardon today. In Teshuvah 3, he has a Migo (he could have said that he didn't pardon today), but we don't force one to pay due to a Migo. Tosfos and the Rosh say so even regarding a document.

Rebuttal (Shach ibid.): Tosfos and the Rosh say when one has a document, he collects with a Migo. This is not called 'Lehotzi' (removing money from its Chazakah). Mahara Sason should have said that in the first Teshuvah the document or witnesses explicitly say that the pardon included today!

Answer #3 (Shach): Teshuvah 4 says that if he says 'until now', it is a Safek. In Teshuvah 3, he wrote 'until this day', which is like 'until now.' In Teshuvah 4 he wrote 'until Nisan 5', which is like 'until Pesach', i.e. until the start.

Answer #4 (Chasam Sofer Sukah 41b DH v'Ayen): A receipt that says that he pardoned Ad Nisan 5 means that he already (yesterday) pardoned them. If it says 'until today', today he pardons! The receipt does not say what hour it was. The lender has the lower hand, for perhaps it was the end of the day!

Shulchan Aruch (ibid.): If the receipt said that he pardoned all claims against him Ad Achshav (until now), it is a Safek, so he cannot collect.

Teshuvas ha'Rosh (76:4, cited in Beis Yosef 54 DH uvi'Teshuvah she'Achar): It is unclear whether he pardoned until the beginning of the day, or the end. Therefore, he cannot collect.