Menachot 35a
מנחות ל״ה א — ד"ה אָמַר רַבִּי יִצְחָק
Menachot 35a:6
Describes the appearance and construction of tefillin and includes the requirement that the straps be black. It is a central Talmudic source for the halakhic treatment of black retzuot.
אָמַר רַבִּי יִצְחָק: רְצוּעוֹת שְׁחוֹרוֹת הֲלָכָה לְמֹשֶׁה מִסִּינַי. מֵיתִיבִי: תְּפִילִּין אֵין קוֹשְׁרִין אוֹתָן אֶלָּא בְּמִינָן, בֵּין יְרוּקּוֹת בֵּין שְׁחוֹרוֹת בֵּין לְבָנוֹת, אֲדוּמּוֹת לֹא יַעֲשֶׂה, מִפְּנֵי גְּנַאי וְדָבָר אַחֵר. קָתָנֵי מִיהָא, בֵּין יְרוּקּוֹת בֵּין שְׁחוֹרוֹת וּבֵין לְבָנוֹת. לָא קַשְׁיָא: כָּאן – מִבִּפְנִים, כָּאן – מִבַּחוּץ. אִי מִבִּפְנִים, מַאי גְּנַאי וְדָבָר אַחֵר אִיכָּא? זִימְנִין דְּמִתְהַפְכִין לֵיהּ.
Rabbi Yitzḥak says: The requirement that the straps of the phylacteries be black is a halakha transmitted to Moses from Sinai. The Gemara raises an objection from a baraita: One may tie phylacteries only with straps of their same type, i.e., the straps must be made from hide, and it does not matter whether they are green, or black, or white. Nevertheless, one should not make red straps, because this is deprecatory to him, as it looks like he has wounds on his head, and also due to something else, i.e., lest people suspect him of engaging in sexual intercourse with a menstruating woman and getting blood on the straps. The Gemara explains the objection from the baraita: In any event, the baraita teaches that it does not matter whether the straps are green, or black, or white, whereas Rabbi Yitzḥak maintains that it is a halakha transmitted to Moses from Sinai that the straps of the phylacteries must be black. The Gemara answers that it is not difficult. Here, the baraita is referring to the inside of the straps, which touch the body. These may be any color other than red. Conversely, there, when Rabbi Yitzḥak says that the straps of the phylacteries must be black, he is speaking of the outside of the straps. The Gemara raises a difficulty: If the baraita is discussing the inside of the straps, what deprecatory matter or problem of something else is there with straps that are red on the inside? After all, this side is not seen. The Gemara answers: Sometimes his straps become reversed, and therefore these concerns are applicable.


