Tashdid over them ( مّ نّـ ) doing Gunna
is wajib there. Leaving wajib could be sin, so wherever you see
Tashdid over Mim and Noon do Gunna. This is called Wajib Gunna. See
below,
To realize how Gunna should pronounce listen above ayah and
concentrate on blue colored places, all those are Wajib Gunna. If you not yet know or forget what is Gunna see here.
