When the aayah ‘…Allah only wishes to remove all abomination from you, ye members of the Family..’ (Quran 33:33) was revealed, RasoolAllahﷺ called Hazrat Faatima, Imaam Hassan and Imaam Hussayn (radi Allahu anhum) and covered them with a cloak.
Sayyidina Ali (karam Allahu wajhu) was behind himﷺ. So, RasoolAllahﷺ covered him under the cloak as well and then said, “O Allah ! They are my Ahlul Bayt so keep impurity away from them and totally purify them.”
Tirmidhi Al-Jami-us-Sahih, 5/351, #3205
Musnad Ahmad, 6/292
Fadaail As-Sahaaba : Imaam Ahmad bin Hambal, 2/587, #994
Al-Mustadrak Al-Haakim, 2/451, #3558
Mujam Al Kabeer : Imaam Tabarani, 3/54, #2662
Al-Itiqad : Imaam Bayhaqi, p.327