Yazid bin Hayyan (may Allah have mercy on him) narrates: I, Husayn bin Sabrah and Umar bin Muslim went to Sayyiduna Zayd bin Arqam (may Allah be pleased with him). When we sat with him, Husayn bin Sabrah said to him: O Zayd! You saw the Messenger of Allah (peace and blessings be upon him), heard his (peace and blessings be upon him) words and took part in battles with him (peace and blessings be upon him). O Zayd! You have attained much good. O Zayd! Tell us what you witnessed and heard from the Messenger of Allah (peace and blessings be upon him). He said: O my nephew! By Allah, I have grown old, my time is long past, and I have forgotten some of what I used to retain from the Messenger of Allah (peace and blessings be upon him). So whatever I narrate to you, accept it, and whatever I do not narrate, do not burden me with it. Then he said: One day the Messenger of Allah (peace and blessings be upon him) stood up to address us at a watering place called Khumm, which lies between Makkah and Madinah. He (peace and blessings be upon him) praised and extolled Allah, the Mighty and Majestic, gave admonition and reminded (us), then said: "To proceed: O people! I am only a human being; soon the messenger of my Lord will come to me and I will respond to his call. And I am leaving among you two weighty trusts: one of them is the Book of Allah, in which is guidance and light, so take hold of the Book of Allah and cling to it firmly." He (peace and blessings be upon him) urged (people) towards the Book of Allah and encouraged it, then said: "My Ahl al-Bayt! I remind you of Allah concerning my Ahl al-Bayt." He (peace and blessings be upon him) said this three times. Husayn asked him: O Zayd! Who are his (peace and blessings be upon him) Ahl al-Bayt? Are his (peace and blessings be upon him) wives not among his (peace and blessings be upon him) Ahl al-Bayt? He said: "His (peace and blessings be upon him) wives are also among his (peace and blessings be upon him) Ahl al-Bayt, but his (peace and blessings be upon him) Ahl al-Bayt are those for whom charity was made unlawful after him (peace and blessings be upon him)." He asked: Who are they? He said: "They are the family of Ali, the family of Ja'far, the family of Abbas and the family of Aqil." It was asked: Was charity made unlawful for all of these? He said: "Yes."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5009