Major Assimilation (Al-Idgham Al-Kabeer) — Identical and Similar Letters

Definition:
Major Assimilation (Idgham Kabeer): merging a voweled letter into an identical or similar voweled letter following it. Called "major" because of its frequency and because the merged letter carries a vowel.

Rule:
Idgham Kabeer is characteristic of Al-Susi's narration from Abu Amr. In Hafs from Asim, it exists in only one agreed position:
"Ma Salakaakum" [Al-Muddaththir: 42] — first Kaf assimilates fully into second Kaf.

Types:
• Identical letters (Mutamatilain): same articulation point and attributes (e.g., Kaf + Kaf)
• Similar letters (Mutaqaribain): close in articulation point or attributes (e.g., Dhal + Tha)

Quranic Example:
"What led you into Saqar?" [Al-Muddaththir: 42] — the first Kaf assimilates into the second.

Note:
In Hafs, this is the sole instance of Idgham Kabeer — unlike other narrations where it is widespread.