It was narrated that 'Abbad bin 'Abdullah said:
"'Ali said: 'I am the slave of Allah and the brother of His Messenger. I am the greatest teller of the truth (Siddiq Akbar), and no one will say this after me except a liar. I prayed seven years before the people." (ID)
English reference (ID): Vol. 1, Book 1, Hadith 120 (ID)
Arabic reference (ID): Book 1, Hadith 125 (ID)