Invoking Allah for Rain (Istisqaa)

Bukhari :: Book 2 :: Volume 17 :: Hadith 141

Narrated Anas bin Malik

The Prophet never raised his hands for any invocation except for that of Istisqa' and he used to raise them so much that the whiteness of his armpits became visible. (Note: It may be that Anas did not see the Prophet raising his hands, but it is narrated that the Prophet used to raise his hands for invocations other than Istisqa. See Hadith No. 807 & 808 and also see Hadith No. 612, Vol. 5).

Source materials are from the University of Southern California MSA site
Hadith eBooks converted from Imaan Star