as the following Hadith 290. Narrated Abu Huraira: The Prophet ﷺ said, "When a man sits in between the four parts of a woman and did the sexual intercourse with her, bath becomes compulsory." (Using translation from Bukhārī 291)  

عَنِ النَّبِيِّ ﷺ قَالَ «إِذَا جَلَسَ بَيْنَ شُعَبِهَا الْأَرْبَعِ ثُمَّ جَهَدَهَا فَقَدْ وَجَبَ الْغُسْلُ»