Sahih Al Bukhari Hadith Number 1028

Narrated `Abdullah bin Zaid Al-Ansari: The Prophet (peace be upon him) went out towards the Musalla in order to offer the Istisqa’ prayer and when he intended to invoke (Allah) or started invoking, he faced the Qibla and turned his cloak inside out.

15  Invoking Allah for Rain (Istisqaa)
Hadith number 1028
Volume no 2
Chapter: 20 (Facing the Qiblah while offering the Istisqa’ prayer)