And Fatimah, the daughter of Muhammad is my wife and my soul whose flesh is mixed with my flesh and blood. And the grandchildren of the Prophet (Hasnain) are my two children from Fatima. Which of you is so fortunate as I am?
I surpassed all of you in my faith in Allah and the Prophet, while I was still small and had not reached the borderline of physical maturity

Al-Iji, Al-Mawaqif fi ‘Ilm al-Kalam, V.3, page 625 and on page 25, the narration from the Prophet (s.a.w.a.) has been mentioned.

And it is narrated from Baridah (just as it would be mentioned in future sources) that the Holy Prophet (s.a.w.a.) said: "For every Prophet, there was a guardian and heir, and Ali is my guardian and heir."

Dailami, Firduas Al-Akhbar, V.3, page 336, hadith 5009; Ibn Asaker, Tarikh Madinah-Damishq, V.42, page 392; Kharazmi, Al-Manaqib, page 84-85; Ibn Maghazli, Manaqib Ali, page 167; Ibn Hajar al-Asqalani, Fath al-Baari, V.8, page 114.

And in the Book Manaqib Sayedna Ali (Aini, p. 29), it is narrated from Rabi’a that the Messenger of Allah (s.a.w.a.) said to Ali (a.s.): “You are my brother, companion and executor of my will.” And Salman narrates: “O Messenger of Allah, for every Prophet, there was a ‘Wasi’ (executor of will). Who is your ‘Wasi’?” The Prophet (s.a.w.a.) kept silent and did not reply. The next day when he saw me, he said, “O Salman”. I made haste and approached the Prophet (s.a.w.a.). I said, “Yes O Messenger of Allah.”

The Prophet (s.a.w.a.) said: “Do you know who was the ‘Wasi’ of Musa?

I said, Yes. Yehoshua ibn Nun.

He asked me, “Do you know why was he Musa’s ‘Wasi’?”

I said, “Since he was the most learned of all at that time.”

The Prophet (s.a.w.a.) said, “My guardian, the center of my secret and the best person I leave behind who will fulfill my promises and pay my debts is Ali ibn Abi Talib.”

Tabarani, Al-Mu’jam Al-Kabir, V.6, page 221; Haythami, Maj’mah al-Zawaid, V. 9, page 113-114 and also refer to Kharazmi, Al-Manaqib, page 67; Muttaqi Hindi, Kanz al-Ummal, V.11, page 611; Aini, Manaqib Sayedna Ali, page 39; Ibn Marduyeh Esfahani, Al-Manaqib, page 104.