The phrase
וְכָל בַּשָּׁלִשׁ עֲפַר הָאָרֶץ
from ישעיהו מ יב (used in the haftara of Vaeschanan) is very familiar to me from prayers, and I can't think where it's from. Moreover, Google is not helping. Does anyone know where it's found in the prayers? (Not the daily or weekly prayers: it must be from some special-occasion prayer.)