Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings be upon him) said: When a man sits between the four parts of a woman and exerts himself (in intercourse), then ghusl becomes obligatory. In the narration of Abdul Samad and Abu Nu’aim, the words are «ثُمَّجَهَدَهَا».
Hadith Referenceالمنتقى ابن الجارود / كتاب الطهارة / 92