Lam of Lafdh Al-Jalalah — Heavy and Light by Examples
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Level: basic
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Lafdh Al-Jalalah: The name "Allah". Its Lam has two states:
(1) Heavy (Tafkhim): When preceded by Fathah or Dammah.
After Fathah: قَالَ اللهُ، إِنَّ اللهَ، شَهِدَ اللهُ
After Dammah: عَبْدُ اللهِ، رَسُولُ اللهِ، نَصْرُ اللهِ
(2) Light (Tarqeeq): When preceded by Kasrah (original or temporary).
After original kasrah: بِاللهِ، لِلَّهِ، فِي سَبِيلِ اللهِ
After temporary kasrah: قُلِ اللَّهُمَّ
(3) Starting with the word: Always heavy because the wasl-hamza is opened with Fathah.
Rule: Fathah/Dammah → Heavy. Kasrah → Light. Unique to Lafdh Al-Jalalah only.
Source: Matn Al-Jazariyyah verses 86-87 | Hidayat Al-Qari (p. 169) | Ghayat Al-Mureed
Question: How is the Lam pronounced in "قُلِ اللَّهُمَّ", "نَصْرُ اللهِ", and "بِاللهِ"?
Answer: "قُلِ اللَّهُمَّ": light (after temporary kasrah). "نَصْرُ اللهِ": heavy (after dammah). "بِاللهِ": light (after original kasrah)