Sahih Muslim 344
Sahih Muslim · Book 3: The Book of Menstruation · At the beginning of Islam, intercourse did not necessitate ghusl unless semen was emitted, then that was abrogated and ghusl becomes obligatory for intercourse
Abu al. 'Ala' b. al-Shikhkhir said:
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ الْعَنْبَرِيُّ ، حَدَّثَنَا الْمُعْتَمِرُ ، حَدَّثَنَا أَبِي ، حَدَّثَنَا أَبُو الْعَلاَءِ بْنُ الشِّخِّيرِ ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَنْسَخُ حَدِيثُهُ بَعْضُهُ بَعْضًا كَمَا يَنْسَخُ الْقُرْآنُ بَعْضُهُ بَعْضًا .
The Messenger of Allah (ﷺ) abrogated some of his commands by others, just as the Qur'an abrogates some part with the other.