Tamid 27B

הניחא למאן דאמר אבנטו של כהן גדול לא זהו אבנטו של כהן הדיוט. אלא למאן דאמר אבנטו של כהן הדיוט זהו אבנטו של כהן גדול, מאי איכא למימר?

The Talmud explains the difficulty: If one maintains that the Mishnah permits the priests to place the vestments beneath their heads, this works out well according to the one who said that the belt of the High Priest is not the same as the belt of an ordinary priest. Although the belt of the High Priest was made of both wool and linen, the belt of ordinary priests, like the rest of their vestments, were made entirely of linen and did not contain diverse kinds. But according to the one who said that the belt of an ordinary priest is the same as the belt of the High Priest, what is there to say? Since the belt contained diverse kinds, how could the Mishnah possibly permit the priests to sleep upon their vestments?

וכי תימא: כלאים בעליה ולבישה הוא דאסור, אבל מימך תותיה שפיר דמי, והתניא: ״לא יעלה עליך״⁠ – אבל אתה מציעו תחתיך. אבל אמרו חכמים: אסור לעשות כן, שמא תיכרך נימא אחת על בשרו.

And if you would say that with regard to diverse kinds it is only placing the garment upon oneself or wearing it that is prohibited, but as for spreading it beneath you, it is permitted, this explanation is difficult. But isn’t it taught in a baraita: The verse states: “Neither should there come upon you a garment of diverse kinds” (Leviticus 19:19). One should infer as follows: But you may spread a garment of diverse kinds beneath you, in order to lie upon it. The baraita continues: This is the halakha by Torah law, but the rabbis said that it is prohibited to do so, lest a single fiber wrap itself upon his flesh, which would cause him to be in transgression of the Torah prohibition. Accordingly, the priests should not be permitted to place vestments made of diverse kinds beneath their heads.