ציטירנדיקער פּירוש אויף עמוס 1:2

And he tarried It is written in the Sefer Mikhlol, at the end of the section on verb grammar, that the latter mem has a qamaṣ on account of the shalsheleth cantillation, becuase it follows the rule of pausals. And it is masoretically recorded about this that "there are seven cantillation marks of the Thundering and Pausing" [translator's note: meaning, the cantillation mark shalsheleth appears seven times in the Tanakh, namely here, Genesis 24:12, Genesis 39:8, Leviticus 8:23, Isaiah 13:8, Amos 1:2, and Ezra 5:15] . And thus I saw handwritten in some books. But "If he tarries, wait for him" (Habakkuk 2:3) has a pathaḥ on the second mem.