Sahih Bukhari, Chapter: Invoking Allah for Rain (Istisqaa)

Allah's Apostle led the morning prayer in Al-Hudaibiya and it had rained the previous night. When the Prophet (p.b.u.h) had finished the prayer he faced the people and said, "Do you know what your Lord has said?" They replied, "Allah and His Apostle know better." (The Prophet said), "Allah says, 'In this morning some of My worshipers remained as true believers and some became non-believers; he who said that it had rained with the blessing and mercy of Allah is the one who believes in Me and does not believe in star, but he who said it had rained because of such and such (star) is a disbeliever in Me and is a believer in star.' "