and if you are in doubt concerning that which we have sent down to our slave then produce a surah of the like thereof and call your witnesses besides 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