It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "I am leaving among you, after me, two weighty trusts: the Book of Allah, Mighty and Majestic, and my 'itrah, that is, my Ahl al-Bayt; and the two of them will never separate until they come to me at the Pond (Hawd)."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4904