[Avodah] Reciting Shir haMa'alot or 'Al Naharot Bavel before Bentching

[Arie Folger]

The Mishnah Verurah, following Peri Megadim, following Magen Avraham,
quotes the SheLaH, that since it is befitting G"d feaRing people to
recall daily the destruction  of the Beit haMiqdashand be saddened by
it ()from Shul'han 'Arukh Ora'h 'Hayim 1:4, apparently based on Zohar,
at least that is what seems from the SheLaH), therefore it is
customary to recite 'Al Naharot Bavel before Birkat haMazon, and on
days when Ta'hanun is not recited, to say Shir haMa'alot.

The SheLaH, which is in the Sha'ar haOtiot section of the SheLaH,
quotes the Zoharic support for the SA's contention, and says therefore
nohagim to say ...

Was the practice of reciting Shir haMa'alot or 'Al  Naharot Bavel
instituted by the SheLaH, or was it a preexisting minhag? From the
SheLaH's wording ("nohagim"), it seems that we are dealing with a
preexisting minhag. However, I cannot find any sources citing this
minhag, which predate teh SheLaH.

So which is it? Is it teh SheLaH's, or older?

Kol tuv,
-- 
Arie Folger,
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