An expression meaning ‘There is no god (or entity worthy of worship) except Allah’. It is known as the taḥlīl.

 
This phrase, taḥlīl, is a form of dhikr (remembrance) of Allah and testifying to His oneness and supremeness. It is present in the shahādah (declaration of faith) as well as in the adhān (call to prayer) and iqāmah.