Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) said: "The greatest trust in the sight of Allah on the Day of Resurrection is that a man goes in to his wife and she goes in to him (i.e. they are intimate), and then he discloses her secret."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14097