17فَلا تَعلَمُ نَفسٌ ما أُخفِيَ لَهُم مِن قُرَّةِ أَعيُنٍ جَزاءً بِما كانوا يَعمَلونَ(Irfan-ul-Quran)So no one knows what coolness of eyes is kept hidden for them. This will be a reward for those (pious deeds) which they used to do.