א"ר יהושע הרואה טי"ת בחלומו סימן יפה לו מ"ט אילימא משום דכתיב טוב אימא (ישעיהו יד, כג) וטאטאתיה במטאטי השמד חד טי"ת קאמרינןאימא (איכה א, ט) טומאתה בשוליה טי"ת בי"ת קאמרינן אימא (איכה ב, ט) טבעו בארץ שעריהאלא הואיל ופתח בו הכתוב לטובה תחילה שמבראשית עד (בראשית א, ד) וירא אלהים את האור לא כתיב טי"ת
Rabbi Yehoshua says: If one sees the letter tet in his dream, it is a good sign for him. The Gemara asks: What is the reason? If we say that it is because the word good [tov] is written in the Torah and begins with the letter tet, then one could say instead that it is an allusion to the verse: “And I will sweep it with the broom [vetetetiha bemate’ateh] of destruction” (Isaiah 14:23), which also contains the letter tet several times but is referring to punishment. The Gemara answers: We mean that when someone sees one tet in his dream, it is a good sign, but this latter verse contains several.The Gemara asks: This latter statement is problematic, as even according to this explanation, one can say that a single letter tet alludes to the verse: “Her filthiness [tumatah] is in her skirts” (Lamentations 1:9), which begins with the letter tet. The Gemara answers: We mean that when one sees the letter tet together with the letter bet in his dream, it is a good sign for him, as the word tov is written with both. The Gemara asks further: According to this, say that it alludes to the verse: “Her gates are sunk [tave’u] into the ground” (Lamentations 2:9), which begins with the letter tet followed by the letter bet.Rather, it is not merely because it is the first letter of the word good [tov] that it is considered a good omen. Since the Torah initially introduces the letter tet in a context of good, with the word good [tov] itself, it is a good omen. As from the word bereshit, the first word in the Torah, until the verse: “And God saw that the light was good [tov]” (Genesis 1:4), the letter tet is not written anywhere.
Rabbi Akiva said to him: My teacher, allow me to say before you one matter that you yourself once taught me. He said to him: Speak. He said to him: It states with respect to the Festivals: “The appointed seasons of the Lord, which you shall proclaim them [otam] to be sacred convocations (Leviticus 23:2). And it is written: “These are the appointed seasons of the Lord, sacred convocations; you shall proclaim them [otam] in their season” (Leviticus 23:4). And it is written: “These are the appointed seasons of the Lord; you shall proclaim them [otam] to be sacred convocations” (Leviticus 23:37). Three times the verses use the term: Them [otam], which can also be read as you [atem], in plural.This comes to teach: You [atem] are authorized to determine the date of the new month, even if you unwittingly establish the New Moon on the wrong day; you, even if you do so intentionally; you, even if you are misled by false witnesses. In all cases, once the court establishes the day as the New Moon, it is sanctified, and God grants His consent. After hearing this, Rabbi Yehoshua said to him in these words: Akiva, you have consoled me; you have consoled me.
Rav Hutner, Pachad Yitzchak, Pesach, 46 (not available free online)