At a full stop with sukūn, the source lists:
ṭūl with iskān — long madd, final consonant fully silent.
tawassuṭ with iskān — middle madd, full final sukūn.
qaṣr with iskān — short madd, full final sukūn.
This is a classification, not unconditional permission for every word. The madd/līn letter and other conditions still matter.
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Three choices when stopping with sukūn
Madd Lengths and Permissible Combinations — Ṭūl, Tawassuṭ, Qaṣr and Consistency
At a full stop with sukūn, the source lists:
ṭūl with iskān — long madd, final consonant fully silent.
tawassuṭ with iskān — middle madd, full final sukūn.
qaṣr with iskān — short madd, full final sukūn.
This is a classification, not unconditional permission for every word. The madd/līn letter and other conditions still matter.