Sunan an-Nasa'i, Book 1, Hadith 200 (In-Book) ⓘ
It was narrated from Abu Ayyub that the Prophet said: "Water is for Water." [1] [1] That is, water for peforming Ghusl is obligatory when the ejaculation of water (semen) occurs.
أَخْبَرَنَا عَبْدُ الْجَبَّارِ بْنُ الْعَلاَءِ، عَنْ سُفْيَانَ، عَنْ عَمْرٍو، عَنْ عَبْدِ الرَّحْمَنِ بْنِ السَّائِبِ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ سُعَادٍ، عَنْ أَبِي أَيُّوبَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الْمَاءُ مِنَ الْمَاءِ " .
also referenced under: Volume 1, Book 1, Hadith 199 (DarusSalam)