This ayah is part of Surah al-Kawthar, revealed -- as this event's own description states -- in response to al-As ibn Wa'il's mockery after the death of the Prophet ﷺ's infant son Abdullah.
admonishes — This is the closing ayah of Surah al-Kawthar, revealed after al-As ibn Wa'il mocked the Prophet ﷺ as having no surviving sons -- the ayah responds that it is al-As's own line that is truly "cut off."