and if you are in any doubt concerning what we have sent down upon our distinguished bondman bring forth a single surah equal to it and call upon all your supporters other than allah if you are truthful.
وإن كنتم في ريب مما نزلنا على عبدنا فأتوا بسورة من مثله وادعوا شهداءكم من دون الله إن كنتم صادقين