Rabbi Chaim Leiberson writes in "Eretz ha'Chayim" (page 8) that he found in the Sidur ha'Arizal that it is a wonderful Segulah to say "l'Shem Shishah Devarim" before Tefilah.

An earlier source is recorded in the Sefer Teshu'os Chayim, by Rabbi Chaim Halbersberg (Parshas Metzora), who writes in the name of Rav Hai Gaon that it is a Segulah to say the Mishnah "l'Shem Shishah Devarim" before Tefilah.

Kol Tuv,

Dovid Bloom

1) It is worth noting that a lot of books cite the custom of saying this Mishnah before a number of activities (praying, learning Torah, sleeping, saying Birkas ha'Mazon, and even before departing from this world).

The Mesivta edition of Shas, to Zevachim 46b in the "Aliba d'Hilchesa" section at the back, cites a few Sefarim who mention this advice. There is also a sefer "Daf Al ha'Daf" which collects interesting ideas on each page of the Gemara, and on Zevachim 46b he cites many Rabbanim who said this Mishnah at various times of the day.

2) However, the only book I have seen who connects this custom specifically to the Arizal is Eretz ha'Chayim, which I cited in my first answer, and he does not say where in the Sidur Arizal it is mentioned. Also, it is surprising that none of the many other writers who mention this custom actually associate it with the Arizal.

3) In addition, the custom seems to have started hundreds of years before the Arizal (whose lived 1534-1572). I cited above that Rav Hai Gaon (939-1038) said it is a Segulah. It may be, therefore, that the custom does not have a strong connection to the Arizal.

4) I did a search on Otzar ha'Chochmah in all the Sefarim that appear under "Sidur ha'Ari" and "l'Shishah Devarim" does not produce any results. The only source that I found that made any reference to the Arizal in connection with l'Shem Shishah Devarim is Eretz ha'Chayim, which I cited in my first answer.

Reb Chaim, which Melaket did you see the source cited in?

Yasher Ko'ach,

Dovid Bloom