Lam negates the imperfect and puts it in the jussive mood. Yufṭir comes from Form IV afṭara, to break a fast; the final sukūn reflects jussive inflection.
In the legal context, this negative construction states that the lone sighting does not license ending the fast.
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Kitab al-Sawm: Eid Crescent Sighting and Testimony
Lam negates the imperfect and puts it in the jussive mood. Yufṭir comes from Form IV afṭara, to break a fast; the final sukūn reflects jussive inflection.
In the legal context, this negative construction states that the lone sighting does not license ending the fast.