Musnad Abu Ya'la al-Mawsili 42:48

Bishr ibn al-Walid narrated to us, Muhammad ibn Talhah narrated to us, from al-A’mash, from ‘Atiyyah ibn Sa’d, from Abu Sa’id, that the Prophet (peace be upon him) said: "I am about to be called, and I will answer. I am leaving among you the two weighty things: the Book of Allah, a rope extended between the heaven and the earth, and my progeny, the people of my house. And the Subtle, the All-Aware has informed me that they will never separate until they return to me at the Basin. So look at how you succeed me regarding them."