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

Anas I said, "While Allah's Apostle (p.b.u.h) was delivering the Friday Khutba (sermon) a man came and said, 'O Allah's Apostle! Rain is scarce; please ask Allah to bless us with rain.' So he invoked Allah for it, and it rained so much that we could hardly reach our homes and it continued raining till the next Friday." Anas further said, "Then the same or some other person stood up and said, 'O Allah's Apostle! Invoke Allah to withhold the rain.' On that, Allah's Apostle I said, 'O Allah! Round about us and not on us.' " Anas added, "I saw the clouds dispersing right and left and it continued to rain but not over Medina."