Arabic definite article
If the word onto which "al"- is prefixed starts with a hamza, the vowel from that hamza may transfer to the lām of "al"- after which the hamza not be pronounced. See Allah in "Arabic definite article" for an example. If this hamza is volatile, that is required. An example is in the phrase "bi’sa al-ismu". The phrase is read as "bi’sa lismu" (Qur'an 49:11). The rule relates to hamza and is not in direct relation to "al"-. Moreover, it is a rare occurrence and is almost never applied in spoken varieties of modern or classical Arabic.