Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates: "The Messenger of Allah (peace and blessings be upon him) prayed for rain, and the people received so much rain that the valley of Qanat flowed for forty days." Then in the morning the people began saying: Such-and-such star has proved true; and some of them said: This is a mercy from Allah which He has sent down.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12825