It is narrated from Abdullah bin Salam (may Allah be pleased with him), he states: It is near that rain will fall continuously in Madinah for forty nights, so that none of the mud roofs of the people of Madinah will remain intact.
Hadith Referenceمسند الإمام الشافعي / كتاب العيدين والأضاحي والاستسقاء / 528
Hadith Takhrijاسناده ضعیف لضعف من لا يتهمه الشافعي وهو ابراهيم بن محمد : اخرجه البيهقي في المعرفة السنن والآثار (2046)۔