It is narrated from Sayyidah Aishah (may Allah be pleased with her) that one day, early in the morning, the Messenger of Allah (peace and blessings be upon him) came out wearing a black cloak with patterns like camel saddles. Hasan (may Allah be pleased with him) came, and he (peace and blessings be upon him) brought him in (under the cloak); then Husayn (may Allah be pleased with him) came, and he (peace and blessings be upon him) brought him in with him too; then Sayyidah Fatimah (may Allah be pleased with her) came, and he (peace and blessings be upon him) brought her into his cloak too; then Ali (may Allah be pleased with him) came, and he (peace and blessings be upon him) covered him with himself in the cloak too. Then he said: "Allah only wishes to remove impurity from you, O people of the household, and to purify you thoroughly [Surah al-Ahzab: 33]."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2858