Q. What is the source for saying Parshas Haman on the third day of the week of Beshalach? Is this an accepted segula for parnassa that one should follow?

A. The Tur and Beis Yosef (O.H. 301), as well as the Mishna Berura (1: 13) mention that it is a segula (remedy and protection)for parnassa, support and livelihood, to recite the Parshas Hamon every day. Perisha and Mishna Berura quote the Yerushalmi Brochos that maintains that one who reads Parshas Hamon every day, is assured that his sustenance will not be diminished. The reason is to inculcate the belief that parnassa is Heavenly given, and just like by the omer of mon, working harder and collecting more, did not contribute to a greater degree of sustain or wealth. They also mention that it could be recited on Shabbos.
Yalkut Menachem quotes that Rebbe Menachem Mendel of Rimanov zt”l asserted that it is a Segulah for Parnassah to recite Parshas Hamon on the Tuesday of Parshas Beshalach. (See Nitei Gavriel ”“ Purim 1: 3). This minhag has become recently, due to social media communication, more popular.
Horav Shlomo Miller Shlit’a opinion is that one should follow the Tur and Poskim mentioned and his family minhogim. When recited on Shabbos, one should not add the accompanying tefilos for parnosso said during the week.

Rabbi Abraham Bartfeld as advised by Horav Shlomo Miller Shlit’a