The prayers were originally fifty, washing from major ritual impurity required seven washings, and washing from urine required seven washings. The Messenger of Allah ﷺ kept asking until the prayers were made five, washing from major ritual impurity became one washing, and washing from urine became one washing.
حدثنا حسين بن محمد حدثنا أيوب بن جابر عن عبد الله يعني ابن عصمة
كانت الصلاة خمسين والغسل من الجنابة سبع مرار والغسل من البول سبع مرار فلم يزل رسول الله ﷺ يسأل حتى جعلت الصلاة خمسا والغسل من الجنابة مرة والغسل من البول مرة