Muwatta Malik (Yahya)

Imam Malik, may Allah have mercy on him, said: Its meaning is that when a man stays in the woman's house, and then there is a dispute, the woman says that he had intercourse with me, and the man says he did not, then the man's statement will be accepted. And if the woman stays in the man's house, and then there is a dispute, then the woman's statement will be accepted.

It reached Imam Malik (may Allah have mercy on him) that Sa'id ibn al-Musayyib used to say: When a man goes to a woman's house, the man's statement will be accepted, and when a woman goes to a man's house, the woman's statement will be accepted.