Sayyiduna Anas (may Allah be pleased with him) narrated that the Prophet (peace and blessings be upon him) would not raise his hands for any supplication except for the supplication of Istisqa (prayer for rain), and in Istisqa he would raise his hands so much that the whiteness of his armpits would become visible.
Hadith Referenceاللؤلؤ والمرجان / كتاب صلاة الاستسقاء / 516
Hadith Gradingمحدثین:«صحیح»
Hadith Takhrij«صحیح، أخرجه البخاري في: 15 كتاب الاستسقاء: 22 باب رفع الإمام يده في الاستسقاء»