Tafsir of Al-Ghashiyah 88:12

Within it is a flowing spring. It is said that its water flows and does not cease. The non-cessation is either derived from the description of the "spring" (ʿayn), because it is [by definition] flowing water; thus, describing it as flowing denotes emphasis, as in [the expression] "a scorching fire." Or, it is derived from the active participle (jāriyah), for it denotes continuity, given the context. The use of the indefinite form is for magnification. Al-Zamakhshari chose the view that it denotes plurality—as in the verse "a soul shall know" (ʿalimat nafs)—meaning many springs whose waters flow.