Hadith 1178
Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates this statement of the Prophet (peace and blessings be upon him): "When a man sits between the four parts of a woman and exerts himself upon her (i.e., has intercourse with her), then ghusl becomes obligatory." In the narration of the narrator named Matar, these words are present: "Even if he does not ejaculate."