The active imperfect يَقُولُ underlies the imperative قُلْ and prohibition لَا تَقُلْ. Jussive formation creates a setting in which the hollow middle radical drops.
قُلْ حَقًّا — speak truth.
لَا تَقُلْ بَاطِلًا — do not say something false.
Here لا is prohibitive and takes a jussive imperfect. It should be distinguished from ordinary negative indicative لا يقولُ, which expresses “he does not say.”
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Commands and Prohibitions from قَالَ
Hollow Verbs: Seven Iʿlāl Rules and Three Short Paradigms
The active imperfect يَقُولُ underlies the imperative قُلْ and prohibition لَا تَقُلْ. Jussive formation creates a setting in which the hollow middle radical drops.
قُلْ حَقًّا — speak truth.
لَا تَقُلْ بَاطِلًا — do not say something false.
Here لا is prohibitive and takes a jussive imperfect. It should be distinguished from ordinary negative indicative لا يقولُ, which expresses “he does not say.”