Al-Adab Al-Mufrad, Book 33, Hadith 766 (English) ⓘ
Ibn al-Kawwa' asked 'Ali about the Milky Way. He said, "It is the water-trough (or loop of the bag) from which the heaven opens up flowing water."
حَدَّثَنَا الْحُمَيْدِيُّ، قَالَ: حَدَّثَنَا سُفْيَانُ، عَنِ ابْنِ أَبِي حُسَيْنٍ وَغَيْرِهِ، عَنْ أَبِي الطُّفَيْلِ سَأَلَ ابْنُ الْكَوَّا عَلِيًّا عَنِ الْمَجَرَّةِ، قَالَ: هُوَ شَرَجُ السَّمَاءِ، وَمِنْهَا فُتِحَتِ السَّمَاءُ بِمَاءٍ مُنْهَمِرٍ.
also referenced under: Hadith 766 (Reference) & Book 33, Hadith 13 (In-Book)