There is a custom of eating black buckwheat on this Shabbat.

On Shabbat B'shalach 5621 (1861) the Tzemach Tzedek said the maamar R'u ki Hashem printed in Likutei Torah. Shortly afterward he said to his son, my grandfather: On Shabbat B'shalach 5565 (1805) my grandfather said this maamar. Afterwards he sent for me and told me that in 5529 (1769) when he was in Mezritch the Maggid had summoned him to his room and had said:

On Shabbat B'shalach 5516 (1756) the Baal Shem Tov said a Maamar on Vayashav hayam...l'eitano,1 "The Red Sea returned to its strength," quoting the Rabbinic play on the last word, l'eitano - litnao, meaning to its condition or agreement.2 In 5521 (1761), a year after the Baal Shem Tov's passing, my Rebbe (the Baal Shem Tov) came to me, said the maamar, and added an explanation of the subject "doing His will" in contrast to "doing His word." And today my Rebbe again came to me to repeat the maamar.

Then the Maggid repeated the maamar to the Alter Rebbe, adding an interpretation of "River Ginai, part for me,"3 which is similar to k'riat yam suf, the splitting of the Red Sea.

The Tzemach Tzedek concluded: Today the Baal Shem Tov, the Maggid and the Alter Rebbe came to me, each repeating the maamar in his own style.

Several hours later the Tzemach Tzedek called my grandfather again and told him an interpretation of the maamar.