Tafsir of Al-Mursalat 77:15

"Woe, that Day, to the deniers"—that is, on that momentous Day. "Woe" (wayl) is, in its origin, a verbal noun meaning destruction; it is rightfully in the accusative case by a verb expressed or implied. However, it is put in the nominative case as an initial subject (mubtada’) to signify the persistence and perpetuity of destruction for the one against whom it is invoked. "That Day" (yawma’idhin) is its adverb of time or its modifier; thus, the justification for beginning the sentence with it is clear. The well-known view is that the justification for this is that it is intended as an invocation (du’a’), as in the phrase: "Peace be upon you" (salamun ‘alaykum).