"They will be served with a cup," and it refers to wine.
Muhammad said: A cup (ka's) is a name that applies to every vessel along with its drink.
"From a flowing spring (ma'in)," and the ma'in is that which is flowing and visible.
﴿يُطَاف عَلَيْهِم بكأس﴾ وَهِي الخَمْرُ.
قَالَ محمدٌ: الكأس اسْمٌ يَقع لكل إناءٍ مَعَ شرابه.
﴿من معِين﴾ والمعين: الْجَارِي الظَّاهِر
