Mishkat al-Masabih #1429

Anas said that when they experienced a drought ‘Umar b. al-Khattab prayed for rain by virtue of al-‘Abbas b. ‘Abd al-Muttalib, and said, "O God, we used to supplicate Thee by virtue of our prophet and Thou didst give us water. We are now supplicating Thee by virtue of our prophet’s uncle, so give us water.” He said that they were then given water. Bukhari transmitted it.