(3) Purification
كتاب الطهارة
(6c) Chapter: Washing - Section 3
(5) باب الغسل - الفصل الثالث
Mishkat al-Masabih 448 
Ubayy b. Ka'b said that “Water is necessary only when there is an emission” was a licence granted in the early days of Islam, but that afterwards it was renounced. Tirmidhi, Abu Dawud and Darimi transmitted it.
عَنْ أُبَيِّ بْنِ كَعْبٍ قَالَ: إِنَّمَا كَانَ الْمَاءُ مِنَ الْمَاءِ رُخْصَةً فِي أَوَّلِ الْإِسْلَامِ ثمَّ نهي عَنْهَا
 صَحِيح  (الألباني)حكم :
Reference : Mishkat al-Masabih 448
In-book reference : Book 3, Hadith 152