Imam Ali (AS) said: "By Allah, I am the Brother of the Messenger of Allah and his friend and his cousin and the inheritor of his knowledge. Who has a better title for succeeding him than me?
Sunni references:
al-Khasa'is al-Alawiyyah, al-Nisa'i
al-Mustadrak, by al-Hakim v3, p112
al-Dhahabi in his Talkhis of al-Mustadrak has admitted the above words to be genuine.
Musnad Ahmad Ibn Hanbal, v5, p40