It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you goes to his wife, let him cover himself, and let the two of them not become fully naked like two donkeys."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10405