The ruling that water is required only after the emission of water was a concession granted in the early days of Islam, then it was abrogated.
حدثنا أحمد بن منيع حدثنا عبد الله بن المبارك أخبرنا يونس بن يزيد عن الزهري عن سهل بن سعد
إنما كان الماء من الماء رخصة في أول الإسلام ثم نهي عنها
[Sahih] Ibn Majah also recorded it in the Book of Purification, Chapter on what has been reported regarding the obligation of ghusl when the two circumcised parts meet, hadith no. 609, from the hadith of Yunus with the same wording. Abu Hazim also narrated it from Sahl bin Saad, found in Abu Dawud, hadith no. 215, and Ibn Khuzayma graded it sahih, hadith nos. 225, 226, as did Ibn Hibban (al-Ihsan), 1170, 1176, and Daraqutni, 1/126, hadith no. 450, and Bayhaqi, 1/165.