"And say, 'Truth has come,'" which is the Quran, ""and falsehood has departed,'" which is Iblis; this is the tafsir of Qatada. ""Indeed is falsehood, ever vanishing (zahouqan)."" The word 'zahouq' means that which is evanescent and passing away.
﴿وَقل جَاءَ الْحق﴾ وَهُوَ الْقُرْآن ﴿وزهق الْبَاطِل﴾ وَهُوَ إِبْلِيسُ؛ هَذَا تَفْسِيرُ قَتَادَةَ ﴿إِن الْبَاطِل كَانَ زهوقا﴾ الزهوق: الداحض الذَّاهِب.
