Sahih Muslim Book 31, Hadith Number 5955.

‘Aisha reported that Allah’s Apostle (may peace be upon him) went out one morning wearing a striped cloak of the black camel’s hair that there came Hasan b. ‘Ali. He wrapped him under it, then came Husain and he wrapped him under it along with the other one (Hasan). Then came Fatima and he took her under it, then came ‘Ali and he also took him under it and then said: Allah only desires to take away any un-cleanliness from you, O people of the household, and purify you (thorough purifying)