In نَصْرُ اللَّهِ, the preceding rāʾ has ḍammah, so the lām of Allah is heavy (tafkhīm).
In دِينِ اللَّهِ, the preceding nūn has kasrah, so the divine-name lām is light (tarqīq).
The written divine name is the same; its preceding vowel determines the pronunciation. Recite the two back-to-back.
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Divine-name lām: heavy and light
Al-Kāfirūn and An-Naṣr: Applied Madd, Idghām, Ghunnah and Waqf
In نَصْرُ اللَّهِ, the preceding rāʾ has ḍammah, so the lām of Allah is heavy (tafkhīm).
In دِينِ اللَّهِ, the preceding nūn has kasrah, so the divine-name lām is light (tarqīq).
The written divine name is the same; its preceding vowel determines the pronunciation. Recite the two back-to-back.