In this construction, لَا is non-governing.
That means it makes the meaning negative but does not change the displayed Mudhaari' form.
With negationBefore negation
لَا يَفْعُلُيَفْعُلُ
لَا يَفْعُلَانِيَفْعُلَانِ
لَا تَفْعُلِينَتَفْعُلِينَ
The vowels, letters, and final Noons remain as they were before لَا was added.
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Negative Present Tense (Mudhaari' Manfi) - Active and Passive
In this construction, لَا is non-governing.
That means it makes the meaning negative but does not change the displayed Mudhaari' form.
With negationBefore negation
لَا يَفْعُلُيَفْعُلُ
لَا يَفْعُلَانِيَفْعُلَانِ
لَا تَفْعُلِينَتَفْعُلِينَ
The vowels, letters, and final Noons remain as they were before لَا was added.