Most beginners meet idgham as one of the four noon sakinah rules. That is a good place to start, but the idea is wider. Any time a letter with sukoon runs into a similar letter, Arabic tends to fold them together. This guide covers all the main cases you will see in the mushaf.

What merging sounds like

When idgham happens, the first letter disappears and the second one is pronounced with a shaddah. In مِنْ رَبِّهِمْ, there is no "n" at all. You read mir-rabbihim, as if the ر were doubled. Many mushafs show this by leaving the first letter without a sukoon and putting a shaddah on the second.

1. Idgham of noon sakinah and tanween

The six letters are gathered in يَرْمَلُونَ.

With ghunnah: ي ن م و

The noon merges but its nasal sound stays for two counts. Because a trace of the noon remains, this is called incomplete idgham (idgham naqis) before ي and و, and complete before ن and م.

• فَمَنْ يَعْمَلْ مِثْقَالَ ذَرَّةٍ خَيْرًا يَرَهُ (az-Zalzalah 99:7), which has two examples in one verse
• مِنْ نِعْمَةٍ
• مِنْ مَاءٍ
• مِنْ وَالٍ (ar-Ra'd 13:11)

Without ghunnah: ل ر

The noon disappears completely: وَلَمْ يَكُنْ لَهُ (al-Ikhlas 112:4), مِنْ لَدُنْهُ, غَفُورٌ رَحِيمٌ, مِنْ رَبِّكَ.

2. Identical letters (mutamathilayn)

When a letter with sukoon is followed by the same letter with a vowel, they merge into one letter with shaddah.

• اضْرِبْ بِعَصَاكَ (al-Baqarah 2:60): two ب
• وَقَدْ دَخَلُوا (al-Ma'idah 5:61): two د
• لَهُمْ مَا: two م, which is the same as idgham shafawi
• رَبِحَتْ تِجَارَتُهُمْ (al-Baqarah 2:16): two ت

There is one important exception. If the first letter is a madd letter (a و or ي stretching the vowel before it), there is no merging. In قَالُوا وَهُمْ and فِي يَوْمٍ, you stretch the madd and then say the second letter separately.

3. Same exit point (mutajanisayn)

These letters come from the same place in the mouth but have different qualities. In the recitation of Hafs, idgham happens in these pairs:

The ط into ت case is special. In بَسَطْتَ the ط merges, but its heaviness (itbaq) stays. You hear a full, heavy start that finishes on a light ت. This is an incomplete idgham, and it is one of the details a teacher will listen for.

4. Neighbouring exit points (mutaqaribayn)

These letters come from places close to each other:

• ل into ر: قُلْ رَبِّ, بَلْ رَفَعَهُ اللَّهُ (an-Nisa 4:158)
• ق into ك: أَلَمْ نَخْلُقْكُمْ (al-Mursalat 77:20). Most teachers in the Hafs tradition read it with complete merging, nakhlukkum.
• The ل of ال into the sun letters: الشَّمْسُ، الرَّحْمَٰنِ. This is the rule of lam shamsiyyah.

Where Hafs does not merge

In كَلَّا بَلْ رَانَ (al-Mutaffifin 83:14) and وَقِيلَ مَنْ رَاقٍ (al-Qiyamah 75:27), Hafs makes a short silent pause (sakt) on the first letter, so there is no idgham even though the letters would normally merge. Most mushafs print a small س there as a reminder.

How to approach all this as a beginner

You do not need to memorise the technical names to read correctly. Most of these merges happen naturally once your makharij are right and you read the mushaf's marks carefully. A useful order is:

1. Master the noon sakinah idgham first, because it is the most common.
2. Learn the madd exception for identical letters, because it is the one people get wrong.
3. Learn the handful of mutajanisayn and mutaqaribayn examples as a list, since there are only a few patterns.

Our teachers cover idgham as part of the Quran with Tajweed course, using exactly these verses so students hear each case in context.