Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates: Allah, the Blessed and Exalted, sends the winds and they carry water from the sky; then they pass through the clouds, and it flows just as milk flows from the udders; then that rain falls.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6487