TASHLUMIN MUST BE RIGHT AFTER THE CURRENT TEFILAH [Tefilah:Tashlumin]
26a (R. Yochanan): If one mistakenly omitted Ma'ariv, he prays (Shemoneh Esreh in) Shacharis twice. If he mistakenly omitted Shacharis, he prays Minchah twice.
26b (Beraisa): If one mistakenly omitted Minchah on Shabbos, he prays two weekday Tefilos on Motza'ei Shabbos. He says Havdalah in the first, but not in the second.
If he said Havdalah in the second and not in the first, he was Yotzei only the second Tefilah.
Inference: Since he did not say Havdalah in the first, it is as if he did not pray (the first).
Contradiction (Beraisa #2): If (in winter) one forgot to mention or request rain, he must go back;
If he forgot Havdalah, he does not go back, for he can say Havdalah later with wine.
This is left difficult.
30b (Rav Huna and Rav Chisda): If one will pray twice in succession, he must pause in between until his mind is settled.
31a (Beraisa): One may not start to pray amidst sadness, laziness... or idle talk, rather, amidst the Simchah of a Mitzvah.
Rambam (Hilchos Tefilah 3:8): If one omitted a Tefilah in its time, due to forgetting, Ones or distraction, he compensates at the next time for Tefilah. First he prays the Chovah (current Tefilah), and then the Tashlumin.
Rosh (4:2, citing Rav Hai Gaon): The Gemara remained with a difficulty. It is not a refutation. He was not Yotzei when there is a Giluy Da'as (revelation) that he intended the first for Tashlumin, e.g. he said Havdalah only in the second.
Tosfos (Berachos 31a DH Rabanan): We pray only amidst seriousness and Simchah of Mitzvah, e.g. Divrei Torah. Therefore, the custom is to say Pesukei d'Zimrah and Ashrei before Tefilah.
Rivash (140): If one forgot to pray Minchah and he prays Ma'ariv twice to compensate, he says Ashrei between the two Tefilos. This shows that the (second) Tefilah is Tashlumin for Minchah. Also, Chazal taught that one who says Tehilah l'David three times a day is a Ben Olam ha'Ba. If one said it only twice during the day, what loss is there to complete the omission at night?! We do not say 'since the day passed (one cannot compensate)', just like we do not say so about Shemoneh Esre. There is no reason not to say it. It is no worse than reading in the Torah. Orchos Chayim obligates pausing between the two Tefilos. What is wrong if he says Ashrei in between, to enter Tefilah amidst Divrei Torah?!
Shulchan Aruch (OC 108:1): If one omitted Shacharis due to a mistake or Ones, he prays Minchah twice. The first Tefilah is Minchah and the second is Tashlumin. If he switched the order, he must pray Tashlumin again. The same applies whenever one must pray Tashlumin.
Darchei Moshe (1): The Gemara implies that if he intended that the first be for Tashlumin, he was not Yotzei.
Magen Avraham (2): The Shulchan Aruch is difficult. The Rosh said that he was not Yotzei when there is a Giluy Da'as that he intended the first for Tashlumin, but not due to mere intent. If not for the Darchei Moshe, we could say that also here he was Megaleh Da'as, e.g. he prayed first without Ashrei, and then said Ashrei and Shemoneh Esre, like we do for Minchah. In any case, this requires investigation. A Giluy Da'as is only if it is evident from the Tefilah itself, e.g. he did not say Havdalah.
Shulchan Aruch (2): If one erred and omitted Minchah, he prays Ma'ariv once for Ma'ariv, and again for Tashlumin. If one omitted Ma'ariv, he prays one Tefilah for Shacharis, and again for Tashlumin. He says Ashrei in between.
Magen Avraham (4): The Shulchan Aruch connotes that we do not say Tachanun in between. If we did, this would be a sufficient break in between. The Levush says so. Divrei Chamudos says that we say Tachanun in between.
Eliyahu Rabah (2): Divrei Chamudos holds that it is better to say Tachanun after the obligatory Tefilah. Afterwards he says Ashrei, Tashlumin, la'Menatze'ach and u'Va l'Tziyon. The Shulchan Aruch mentioned only Ashrei (even though also Tachanun is in between) because we always say it.
Machatzis ha'Shekel (DH v'Lechem): When we say Tachanun, no other break is needed in between. We say Ashrei after the Tashlumin.
Mishnah Berurah (10): The Magen Avraham forbids eating before the Tashlumin, but if he began, he need not interrupt. Machatzis ha'Shekel and Magen Giborim say that he must cease, for one must pray Tashlumin as close to the Chovah as possible.
Mishnah Berurah (11): One may not even learn between the Tefilos. However, he may hear Chazaras ha'Shatz, for this is engaging in Tefilah.
Mishnah Berurah (12): He says also Tachanun in between, for we do not separate Tachanun from Shemoneh Esre.
Kaf ha'Chayim (19): When one says Ashrei in between the Tefilos, he intends that it is only to pray amidst praise. After the Tashlumin, he says Ashrei again in its proper place (after Tachanun, and before u'Va l'Tziyon).
Rema: Similarly, when one prays Ma'ariv twice to compensate for Minchah, he says Ashrei in between.
Bach (DH Kasav): Semak taught that we say Ashrei in between two Tefilos at Shacharis or Ma'ariv. In the latter case, Ashrei is in order to enter Tefilah amidst Divrei Torah. This connotes that when he prays Minchah twice, he need not say Ashrei in between. The Ashrei before Minchah exempts also the Tefilah for Shacharis.
Note: If so, why doesn't Keri'as Shema before Ma'ariv exempt also Tashlumin for Minchah?
Bach (ibid.): However, the Gemara (30b) says that one waits between one Tefilah and another the time to walk four Amos. If he must say Ashrei in between, it is more! Perhaps the Shi'ur of four Amos applies only to (between Shacharis and) Musaf, which is only seven Berachos. Ashrei was enacted only for 18 Berachos. Rashi and the Tur explain that the Shi'ur of waiting applies also to Tashlumin. This is even if he will not say Ashrei in between, but l'Chatchilah Semak obligates saying Ashrei in between. However, regarding praying Ma'ariv twice, the Rikanti (Vayera 25:4) warned not to say Ashrei after praying Minchah.
Taz (3): Why didn't Semak mention Ashrei before Tashlumin for Shacharis? Surely he requires it, for the same reason applies! It seems that he needed to teach about Ashrei in between at Ma'ariv and Shacharis. Had he taught only at Shacharis, one might have thought that since in any case he must say Ashrei before la'Menatze'ach, he says it in between, but not at Ma'ariv, in which we do not say Ashrei. He taught about Ma'ariv, and the same applies to Tashlumin after Minchah. Had he taught about Minchah, one might have thought that Ashrei is in place of his omission of Ashrei after Shemoneh Esreh of Shacharis (he did not pray at all), but it is not needed before Tashlumin for Minchah. Had he taught only about Minchah and Ma'ariv, one might have thought that also at Shacharis he needs only the Ashrei between the two Tefilos, since we learn from Ma'ariv. He teaches that this is not so.
Mishbetzos Zahav: The Bach and Taz say that Ashrei is in order to enter Tefilah amidst Divrei Torah, and also to separate the Tefilos. The Rivash brought a third reason, so it will be clear that the extra Ma'ariv is Tashlumin for Minchah. Based on the third reason, we would say Ashrei in between at Shacharis (for in any case we say it before la'Menatze'ach) and at Ma'ariv (to show that the latter is Tashlumin for Minchah), but not at Minchah. Had the Rema taught only about at Ma'ariv, one might have thought that at Shacharis, it suffices to say Ashrei between the Tefilos, but we need not repeats Ashrei between the Tashlumin and la'Menatze'ach. Had he taught only about at Minchah, one might have thought that it is in order to say Ashrei three times every day.
Magen Avraham (5): The Bach says that the Rikanti warned strongly not to say Ashrei after Minchah. In Parshas Vayera, he says not to say it in Ma'ariv. If one comes to Minchah when the Tzibur started Shemoneh Esre, he prays with them and say Ashrei afterwards, unlike the Bach. Also Hagahos Maimoniyos and Sefer Chasidim (812) say so. The custom is to say Ashrei after Minchah on Yom Kipur. The Zohar connotes that we do not say it. I say that Yom Kipur is different, for the entire day is b'Ratzon (Tefilos are accepted). The Zohar connotes that one may say it without intent for an obligation.
Gra: We say Ashrei in order to pray amidst Divrei Torah. Since in any case we must say Ashrei, we say it now (in between). This is why the Rema says 'similarly', i.e. even though one need not say Ashrei now, he says it for the Tashlumin, for he omitted both Ashrei with Minchah. Letter of the law, one must wait only the time to walk four Amos in between Tefilos (105:1).
Mishnah Berurah (13): The Acharonim say that l'Chatchilah, one says Ashrei also between Minchah and Tashlumin for Shacharis.
Mishnah Berurah (14): Some Acharonim bring from Mekubalim not to say Ashrei at Ma'ariv, even to compensate for Minchah. Whatever one does, he has whom to rely on. As long as it is day, he should say it, even if it is after Minchah. The Magen Avraham bring from the Zohar that he should not intend for his obligation, rather, like one who says Tehilim.
Kaf ha'Chayim (20): Many say that we say Ashrei in between at Minchah, but not at Ma'ariv. Chesed la'Alafim and Ben Ish Chai forbid also at Minchah, for we do not say Ashrei after Minchah. It is proper to rule like this, for there is no Chiyuv to say Ashrei. It is only l'Chatchilah. Therefore, it is best to be passive (and not say it).