Sayyiduna Usamah bin Zayd (may Allah be pleased with them both) said: The Prophet (peace and blessings be upon him) sent me to Uthman (may Allah be pleased with him) with a bowl of meat. I went in to him and Ruqayyah (may Allah be pleased with her) was sitting there. I have never seen two people more beautiful than them (may Allah be pleased with them both). I would look at Ruqayyah one moment and at Uthman the next. When I returned, the Prophet (peace and blessings be upon him) asked me: "Did you go in to them?" I said: "Yes." He (peace and blessings be upon him) asked: "Have you seen a couple more beautiful than them?" I said: "No, O Messenger of Allah. I kept looking at Ruqayyah one moment and at Uthman the next."
Imam al-Tabarani (may Allah have mercy on him) said: This incident was before the revelation of the verse of hijab.
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 96