In الْأَبْتَرُ, the definite-article lām is pronounced because hamzah is a moon letter. Its internal bāʾ has sukūn and therefore qalqalah, without adding a fresh vowel.
In الْكَوْثَرَ, an unvowelled wāw follows fatḥah, making it a ḥarf līn, not a normal madd wāw. A madd wāw requires preceding ḍammah. Inspect the internal vowels, not just the shape of the letter.
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Al-Kawthar: lām, bāʾ and a soft letter
Applied Tajwīd Diagnostics: Four Short Sūrahs
In الْأَبْتَرُ, the definite-article lām is pronounced because hamzah is a moon letter. Its internal bāʾ has sukūn and therefore qalqalah, without adding a fresh vowel.
In الْكَوْثَرَ, an unvowelled wāw follows fatḥah, making it a ḥarf līn, not a normal madd wāw. A madd wāw requires preceding ḍammah. Inspect the internal vowels, not just the shape of the letter.