It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) concerning "And We sent down from the rain clouds abundant water" [Surah al-Naba': 14], that what is meant by this blessed verse is: Allah Almighty sends the winds, and they carry water from the sky, and it travels in the form of clouds until it flows just as the milk of a milch she-camel flows. Then it is sent from the sky like water spouts, then the winds turn it (and scatter it), and it comes down to the earth in the form of drops.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6486