Sayyidah Umm Salamah (may Allah be pleased with her) said: I was with the Prophet (peace and blessings be upon him), and Maymunah was with him. Then Ibn Umm Maktum came, and that was after we had been commanded to observe hijab, and he came in upon us. He (peace and blessings be upon him) said: "Both of you, screen yourselves (from him)." We said: O Messenger of Allah! Is he not blind? He can neither see us nor recognise us. The Prophet (peace and blessings be upon him) said: "Are you two blind as well? Do you not see him?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13525