Quran 72.17-20
That We may test them thereby, and whoso turneth away from the remembrance of his Lord; He will thrust him into ever-growing torment. And the places of worship are only for Allah, so pray not unto anyone along with Allah. And when the slave of Allah stood up in prayer to Him, they crowded on him, almost stifling. Say (unto them, O Muhammad): I pray unto Allah only, and ascribe unto Him no partner.