A following istiʿlāʾ letter in the same word can change the treatment of sākin rāʾ after an original kasrah. In قِرْطَاسٌ, the following ط is emphatic, and the book treats the rāʾ as heavy.
The condition “in the same word” matters. Do not extend this rule to every nearby emphatic letter elsewhere in a phrase.
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An istiʿlāʾ letter after sākin rāʾ
Tafkhīm and Tarqīq — Alif, Divine-Name Lām and Rāʾ
A following istiʿlāʾ letter in the same word can change the treatment of sākin rāʾ after an original kasrah. In قِرْطَاسٌ, the following ط is emphatic, and the book treats the rāʾ as heavy.
The condition “in the same word” matters. Do not extend this rule to every nearby emphatic letter elsewhere in a phrase.