While the main forms of certain letters such as alef+lam form a ligature:

لا (no)

إعلان (advertizement) الأب (the father)

the corresponding presentation forms shouldn't ligate:

ﻟﺎ

Related ligatures from pre-formed accented alif forms:

لآ لأ لإ لا
لٱ لٲ لٳ لٵ

as well as ligatures with combining marks:

لٓا لٔا لٕا لٟا
لٓا لٔا لٕا لٟا

and their corresponding final forms:

ملآ ملأ ملإ ملا
ملٱ ملٲ ملٳ ملٵ

The non-ligating corresponding presentation forms are:

ﻟﺎ ﻟﺁ ﻟﺂ ﻟﺃ ﻟﺄ ﻟﺇ ﻟﺈ