Yet another type are the traveling Angels who seek gatherings of dhikr.  It is related that Abū Hurayra radīallahu `anhu said that the Messenger of Allah sallallāhu `alayhi wasallam  said:  Allah Almighty has Angels who roam about seeking the people of dhikr.  When they find a group doing dhikr of Allah, they call to one another, ‘Come to that which you have been seeking!'

The Angels of Dhikr
Shaykh `Abdul Hamid Kishk