"Indeed, the righteous will be among gardens and rivers," meaning all the rivers.
Muhammad said: It is a singular noun that denotes a plural.
﴿إِنَّ الْمُتَّقِينَ فِي جَنَّاتٍ وَنَهَرٍ﴾ يَعْنِي: جَمِيع الْأَنْهَار.
قَالَ محمدٌ: وَهُوَ واحدٌ يدل على جمع.
