In دَآبَّةٍ, the madd alif is followed by بّ. A shaddah entails a first, silent consonantal element followed by a vowelled element. Thus the madd letter meets that first sākin element within the same word.
This is the permitted category ʿalā ḥaddih. Do not erase the actual madd; the subsequent chapter treats the length required in such situations.
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First example: dābbah
Meeting of Two Sākin Letters — ʿAlā Ḥaddih, Ghayr Ḥaddih and Tanwīn
In دَآبَّةٍ, the madd alif is followed by بّ. A shaddah entails a first, silent consonantal element followed by a vowelled element. Thus the madd letter meets that first sākin element within the same word.
This is the permitted category ʿalā ḥaddih. Do not erase the actual madd; the subsequent chapter treats the length required in such situations.