Tafsir of As-Saffat 37:20

The Day of Recompense Allah tells us what the disbeliever will say on the Day of Resurrection; how they will blame themselves and admit that they wronged themselves in this world. When they see the horrors of the Day of Resurrection with their own eyes, they will be filled with regret at the time when regret will not avail them anything

وقالوا يا ويلنا هذا يوم الدين

They will say: "Woe to us! This is the Day of Recompense!'' And the angels and the believers will say:

هذا يوم الفصل الذي كنتم به تكذبون