Sunan an-Nasa'i 199
سنن النسائي#199SahihIt was narrated from Abu Ayyub that the Prophet (ﷺ) said:"Water is for Water." [1] [1] That is, water for peforming Ghusl is obligatory when the ejaculation of water (semen) occurs
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 1:200