Mukhtasar Bukhari

Sayyiduna Anas bin Malik (may Allah be pleased with him) says that the Prophet Muhammad (peace and blessings be upon him) did not raise his hands in any supplication as high as he did in the supplication for rain (Istisqa), and in Istisqa he (peace be upon him) would raise his hands so high that the whiteness of his armpits would become visible.