Full Sharh — Mishkat al-Masabih 417
وَعَن عبد الله بن عمر قَالَ كَانَتِ الصَّلَاةُ خَمْسِينَ وَالْغُسْلُ مِنَ الْجَنَابَةِ سبع مرار وَغسل الْبَوْل من الثَّوْب سبع مرار فَلَمْ يَزَلْ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُسْأَلُ حَتَّى جعلت الصَّلَاة خمْسا وَالْغسْل من الْجَنَابَة مرّة وَغسل الْبَوْل من الثَّوْب مرّة. رَوَاهُ أَبُو دَاوُد
English Translation
Ibn ‘Umar said that the original requirement was fifty times of prayer, seven washings to remove sexual defilement, and seven washings when urine fell on a garment. God’s messenger therefore kept on making requests till five times of prayer were appointed, one washing for sexual defilement, and one washing of a garment because of urine. Abu Dawud transmitted it.
Source
Mishkat al-Masabih(مشكاة المصابيح)
Purification
Hadith Number
417