In وَلَمْ يَكُنْ لَهُ, the final nūn sākinah of yakun is followed by lām in the next word. This calls for idghām without ghunnah, not prolonged nasalization. The nasal form of idghām belongs to yāʾ, nūn, mīm and wāw.
Contrast لَمْ يَلِدْ: here a mīm sākinah precedes yāʾ and remains clearly pronounced through iẓhār shafawī. Do not transfer nūn rules to mīm automatically.
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Al-Ikhlāṣ: nūn sākinah before lām
Applied Tajwīd Diagnostics: Four Short Sūrahs
In وَلَمْ يَكُنْ لَهُ, the final nūn sākinah of yakun is followed by lām in the next word. This calls for idghām without ghunnah, not prolonged nasalization. The nasal form of idghām belongs to yāʾ, nūn, mīm and wāw.
Contrast لَمْ يَلِدْ: here a mīm sākinah precedes yāʾ and remains clearly pronounced through iẓhār shafawī. Do not transfer nūn rules to mīm automatically.