´Ubayy bin Ka'b narrated:` "Water is for water,' was only permitted in the beginning of Islam. Then it was prohibited."
Explanation & Benefits
Shaykh Dr. Abdur Rahman Freywai
1:
And it has been commanded that whether semen is emitted or not, if the circumcised part (glans) meets the circumcised part, then ritual bath (ghusl) becomes obligatory.
Source: Sunan al-Tirmidhi – Majlis ‘Ilmi Dar al-Da‘wah, New Delhi Edition, Page: 110