Abu Ammar (may Allah have mercy on him) says: I was sitting with Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) when the people mentioned Sayyiduna Ali (may Allah be pleased with him) and reviled him. When they had got up, Sayyiduna Wathilah (may Allah be pleased with him) said: "Sit, and I will tell you about this man whom they reviled. One day I was with the Messenger of Allah (peace and blessings be upon him) when Sayyiduna Ali, Sayyidah Fatimah, Sayyiduna al-Hasan and Sayyiduna al-Husayn (may Allah be pleased with them) came, and he (peace and blessings be upon him) cast his cloak over them, then said: 'O Allah, these are my household (Ahl al-Bayt). O Allah, remove impurity from them and purify them thoroughly.' I said: 'O Messenger of Allah, and me too?' He (peace and blessings be upon him) said: 'And you too.'" Sayyiduna Wathilah (may Allah be pleased with him) says: "By Allah, in my view this is the deed of mine I rely on most."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18379