Siman 41

We learn in Bava Metzia (105b): It was taught in a baraita: If one was carrying a load on his head, if the tefillin are crushed—it is forbidden. And if not—it is permitted. Regarding what load did they say this? Regarding a load of four kabin. Rabbi Hiyya taught: One who brings out manure on his head while tefillin are on his head—behold, he may not move them to the sides, nor may he tie them to his hand, because he is treating them with a practice of contempt. But he may tie it on his arm in the place of tefillin. Those of the school of Shila said: Even a cloth of theirs (some versions read "of bread")—it is forbidden to place it on a head that has tefillin on it. And how much? Abaye said: A quarter of a quarter of Pumbedita. Thus far the wording of the Gemara.

It is implied that Rav Shila disagrees with the former. That is to say: even a light burden such as a kerchief is forbidden. And since Abaye explains his words, we rule accordingly. This is the opinion of the Rambam in the fourth chapter, who wrote: One who carries a burden on his head removes the tefillin of the head until he removes the burden. And even a kerchief is forbidden to place on the head that has tefillin upon it. But he may wind his turban over the tefillin. Thus far his words. That is to say: regarding the turban that he always wears on his head, there is no disgrace if the edge of the turban rests upon the tefillin, since this is his garment. And so we practice. On the contrary, through this the tefillin of the head is strengthened so that it does not move from its place. Our teacher, the Beit Yosef, transcribed his words in the Shulchan Aruch and concluded: But a thing that is his way to place on his head, such as a hat or a turban, is permitted. Thus far his words.

But the Rif and the Rosh transcribed both the beraitot and the words of Rav Shila. The Rishonim were precise in saying that they maintain that they do not disagree at all, and they distinguished in their words with various distinctions. There is one who says that the beraita deals with post facto where he is already carrying the burden, or with one whose livelihood is from this; in this case the measure is four kabin. And Rav Shila deals with ab initio, and it is forbidden even with a kerchief, since his livelihood is not from this (Beit Yosef in the name of R. Y. Aboab). But dung is forbidden in any case because of the disgrace, and this is the beraita of Rabbi Hiyya. And there is one who distinguished that the beraita deals with a case where the burden is already on his head and he wants to don tefillin, for then with less than four kabin it is permitted, and only dung is forbidden. And Rav Shila deals with when the tefillin are on his head and he wants to place a burden upon them, for then even a kerchief is forbidden (Beit Yosef). And there is one who explained that the beraita does not deal at all with the burden being on his head, for the burden is slung behind him and tied with a rope on his head, and the rope presses the tefillin when the burden is heavy, four kabin (ibid. in the name of the R. Y. Escandari). And it appears more likely like the first excuse, to distinguish between ab initio and post facto (and so wrote the Bach and the Derisha, see there).

But our teacher, the Rema, wrote in the Shulchan Aruch, and this is his wording: But a thing that is customary to place on one's head, such as a hat or a turban – it is permitted. And even so, if it is a heavy burden of four kabin, and the tefillin are pressed – he must remove them. Thus far his words. And his intention is: that which requires four kabin – this is regarding a thing that is customary to place on one's head. And that which forbids a turban – is regarding a thing that is not customary to place on one's head. And the difficulty is clear, for it is not customary for there to be any object of four kabin on one's head. And there is one who explained to distinguish between crushing and not crushing, that if it crushes the tefillin even a kerchief is forbidden, and if it does not crush it is permitted up to four kabin (Taz, subsection 1). And this is more difficult, for how is crushing relevant to a turban? And there is one who wrote to distinguish between a place where it is customary to carry a burden on one's head, for then it is permitted up to four kabin. And in a place where it is not customary – even a kerchief is forbidden (see Magen Avraham at the beginning of this siman). And in my humble opinion it appears that certainly when he sits in his house even a kerchief is forbidden, for who compels him to do so? And this is the statement of Rav Shila. And the Baraita deals with when he is walking on the way, as is proven by the language "carries a burden on his head." And then it is permitted up to four kabin, only with manure is it forbidden due to disgrace.