Imam Husain b. Ali (a.s.) is reported to have quoted the Messenger of Allah (s.a.w.a.) that he
said: The first thing that the Almighty Allah created was His veil, then He wrote on its hem: There is no god except Allah, Muhammad is the Messenger of Allah and Ali is his successor.

Then He created the Arsh and on its edges He inscribed: There is no god except Allah, Muhammad is the Messenger of Allah and Ali is his successor. Then He created the Tablet (Lauh) and wrote on its perimeter: There is no god except Allah, Muhammad is the Messenger of Allah and Ali is his successor.

Thus whoever claims to love the Prophet but does not love the successor, is a liar. And whoever thinks that he recognizes the Prophet but does not recognize the successor, has resorted to disbelief. Then he said: Know that, my Ahle Bait are means of security for you, so love them. Remain attached to my love and theirs so that you may never go astray. It was said: Who are the Ahle Bait, O Messenger of Allah (s.a.w.a.)?”

He replied: “Ali, my two grandsons (Sibtain) and nine persons from the descendants of Husain (a.s.) are the righteous, trustworthy and infallible Imams. Know that, they are my Ahle
Bait and my Itrah; they are my flesh and blood.
Kefaayah Al-Athar p 310