17. The fourth cup of wine: A. When to drink the 4^th cup of wine:^[1]

Some Poskim^[2] rule that one is required to drink the 4th Cup immediately after completing the blessing of Yishtabach [as follows the Ashkenazi custom to conclude Birchas Hashir with Yishtabach] or immediately after completing the YeHallelukah which is said after concluding Yishtabach [according to the Sephardi custom], prior to saying any of the hymns which are accustomed to be said.^[3] Nonetheless, the custom in these provinces is not like this opinion [and rather they first say the hymns and only then drink the 4th cup of wine].^[4] [Practically, in the Siddur Admur rules like the former opinion that one may not make an interval between the end of Hallel and the drinking of the 4^th cup, and rather immediately after concluding the blessing of Yishtabach he is to drink it.]

  B. Leaning:

Men are required to lean upon drinking the 3rd cup of wine as explained in chapter 3 Halacha 7B. Nonetheless, if one forgot to lean, he does not re-drink the cup, as explained in Chapter 3 Halacha 7E.

C. After blessing:

After drinking at least a Revius of the cup of wine, one is to say an after blessing. [This after blessing likewise includes the wine drunk for the 3rd cup of wine.^[5]]

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[1] Admur 480:3; Siddur Admur; See Kaf Hachaim 480:10

[2] Opinion in Admur ibid; Rashal 88; Bach end of 480; Taz 480:1

[3] The reason: As the sages instituted for the Hallel and Birchas Hashir to be completed over the 4th cup of wine, and if so one may not make an interval between them with hymns they were not part of their institution. [Admur ibid]

[4] Admur ibid; M”A 480:2; Tashbeitz 99 in name of Maharam; Chok Yaakov 480:5

[5] Levush 480; M”B 480:7; Kaf Hachaim 478:14