Silent letters:

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As a general rule, the letters having no sign on them (empty letters) must be treated as silent letters. Since they do not produce any sound of their own therefore, they should be overlooked. These silent letters generally occur when long vowel letters (Madd) Alif waw
and Ya are involved. Also letter Lam frequently becomes silent where the definite article (al) is prefixed to a word beginning with a letter having its Makharaij points of articulation is closed to letter (refer to lesson 31-4 for some examples. (Hurful Samsiyatu)(1) Exception to the silent letter rule is Maddah Alif refer to lesson 11) Some Middle Eastern prints of the Holy Quraan may write these letters differently.

Hurful Samsiyatu letters are: