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