Yazid bin Hayyan Tamimi (may Allah have mercy on him) says that once I, along with Husain bin Sabrah and Umar bin Muslim, went to the service of Hazrat Zaid bin Arqam (may Allah be pleased with him). When we had sat down, Husain said, "O Zaid! You have attained great good. You have seen the Prophet Muhammad (peace be upon him), heard his hadiths, participated in jihad with him, and prayed in his company. Therefore, you have been granted abundant goodness. Please narrate to us a hadith that you yourself heard from the Prophet Muhammad (peace be upon him)." He replied, "Nephew! I have grown old, my time has passed, and of the things I had preserved from the Prophet Muhammad (peace be upon him), I have forgotten some. So, if I narrate a hadith to you according to my ability, then accept it, otherwise do not compel me." Then he said, "One day, the Prophet Muhammad (peace be upon him) stood up to deliver a sermon near a spring between Makkah Mukarramah and Madinah Munawwarah, which is called 'Khumm.' After praising and glorifying Allah, he gave some advice and admonition, then said, 'Amma ba'd (to proceed): O people! I am only a human being. It may be that soon the messenger of my Lord will come to call me, and I will respond to his call. Remember! I am leaving among you two weighty things. The first is the Book of Allah, in which there is guidance and light. So hold fast to the Book of Allah.' Then the Prophet Muhammad (peace be upon him) encouraged and drew attention to acting upon the Book of Allah. And he said, 'The second thing is my Ahl al-Bayt.' And he said three times, 'I remind you by Allah regarding the rights of my Ahl al-Bayt.' Husain asked, 'O Zaid! Who are meant by the Ahl al-Bayt of the Prophet Muhammad (peace be upon him)? Are the pure wives of the Prophet Muhammad (peace be upon him) not included among the Ahl al-Bayt?' He replied, 'The pure wives of the Prophet Muhammad (peace be upon him) are also among his Ahl al-Bayt, but here it means those people upon whom, after the Prophet Muhammad (peace be upon him), charity is forbidden.' Husain asked, 'Who are those people?' He replied, 'The family of Aqil, the family of Ali, the family of Ja'far, and the family of Abbas.' Husain asked, 'Is charity forbidden for all of them?' He replied, 'Yes!'"