A Prohibition Can Use a Third-Person Form

The Prohibitive: Negation, Prohibition and Jussive Endings

Do not assume that every prohibitive must visibly begin with second-person تَ. A prohibition may also be expressed with a third-person form.

لَا يَسْخَرْ قَوْمٌ مِنْ قَوْمٍ
No group should ridicule another group.

Here يَسْخَرْ is a singular masculine third-person imperfect in the jussive state. The surrounding sentence expresses a prohibition.