Siman 54

"Yishtabach" does not open with "Baruch" because it is adjacent to the blessing of "Baruch She'amar." That is to say: "Baruch She'amar" is the blessing before Pesukei D'zimra, and "Yishtabach" is the blessing after Pesukei D'zimra. Therefore, one should not say "Yishtabach" unless he said "Baruch She'amar" and some of Pesukei D'zimra. The conclusion of the blessing is "Chei Ha'olamim." And there one must answer "Amen," and not after "Gadol u'mehulal batishbachot" according to Nusach Sefard. Even though in Hallel we conclude with "Mehulal batishbachot," nevertheless in "Yishtabach" it continues until "Chei Ha'olamim." And one must say "Chei" with a tzeirei and not with a patach. It has already been explained in siman 51, section 4, that even though the opinion of our teacher, the Beit Yosef, is that after "Yishtabach" one may answer "Amen" to his own blessing, like after "Boneh Yerushalayim" in Birkat HaMazon, nevertheless we do not hold accordingly, and the custom is not so. Only regarding this matter is it preferable: that when he finishes simultaneously with the chazzan, he may answer "Amen," see there.

Even though Pesukei D'Zimra and "Yotzer Or" are two distinct matters, and we recite Kaddish between them, nevertheless it is forbidden to interrupt with speech between "Yishtabach" and "Yotzer" because they are all part of the order of the prayer, and they are like one matter. The poskim cited from the Yerushalmi that one who speaks between "Yishtabach" and "Yotzer" – it is a transgression in his hand, and he returns from the battle lines because of this transgression so that it should not prosecute against him. And this is not related to what some are accustomed to say during the Ten Days of Repentance, "Shir HaMa'alot MiMa'amakim" after "Yishtabach," for this is considered like the order of the prayer, just as according to the Rambam they say "Az Yashir" after "Yishtabach" as I wrote in siman 51. And it is not called an interruption except for mundane matters. (And the Magen Avraham, subsection 2, remained in "needs further study," and I do not know why.)

Nevertheless, since they are two distinct matters, they are not entirely comparable to an interruption in the middle of Pesukei D'Zimrah. This is what our teachers, the authors of the Shulchan Aruch, wrote in section 3, and this is their wording: There is one who says that for the needs of the community, or to apportion charity for one who comes to be supported by charity, it is permitted to interrupt. From this spread the custom in many places to bless a sick person, or to lodge a complaint in the beit knesset so that they will perform justice for him, between "Yishtabach" and "Yotzer," for all this is called "for the sake of a mitzvah." Afterward, when they return to pray, the shliach tzibbur shall say a few verses of Pesukei D'Zimrah and say Kaddish over them, for Kaddish is never said without a preceding praise. Therefore, we begin Arvit without Kaddish. Likewise, one who did not have tzitzit or tefillin, and they were brought to him between "Yishtabach" and Kaddish, may don them and recite the blessing over them. But between Kaddish and "Barchu," he shall not interrupt for anything. All the more so, he shall not interrupt after the shliach tzibbur has said "Barchu" before they begin the blessing of "Yotzer." Thus far his words.

The explanation of the matters: Since they are two distinct subjects, it became the custom to interrupt them for a matter of a mitzvah. It would have been appropriate for the interruption to be after the recital of Kaddish, for behold, the Kaddish relates back to the Pesukei D'Zimrah, as there is no Kaddish without a prayer preceding it. If so, how is it possible to interrupt before Kaddish, for how will he say Kaddish afterward without a prayer adjacent to the Kaddish? Nevertheless, the custom is to make the interruption before Kaddish, for the reason that according to the Kabbalah it is forbidden to interrupt at all between Kaddish and "Barchu," and between "Barchu" and "Yotzer." If so, it is necessary to interrupt before Kaddish. And if it is because of the question of what the Kaddish will be said upon, to this he says that in truth the sheliach tzibbur will say some Pesukei D'Zimrah afterward. However, this was in their time. But in our time, we have never heard of making an interruption between "Yishtabach" and Kaddish. All delays of the prayer among us, or any performance of tzedakah, are before the reading of the Torah. And that which they wrote, that when they brought him the tallit and tefillin he should don them between "Yishtabach" and Kaddish, we have already explained in siman 53, section 2, that this is for an individual. But the sheliach tzibbur should don them before "Yishtabach," see there. (And what the Magen Avraham wrote regarding the matter of "Prisat Shema" after the Shemoneh Esreh and after the final Kaddish—we have not heard of this custom now. And in a place where there is a custom—it is obvious that one should not say two Kadishim adjacent to one another without an interruption of psalms between them. And he commanded to be brief with Kadishim, as will be explained at the beginning of siman 55.)