Ibn Asaker, Tarikh Madinah-Damishq, V.42, page 303;

It is narrated from Salem, slave of Hudhaifah that the holy Prophet (s.a.w.a.) commanded us to greet Ali ibn Abi Talib as: "Ya Amirul-Mu'minin Wa Rahmatullahi Wa Barakatuh (O Commander of the believers and Allah’s Mercy and Blessings on you" Aini, Manaqib Sayedna Ali, page 18, and on page 61, it is narrated from Anas as saying: The Messenger of Allah (s.a.w.a.) said, “O Anas! The first person who would come to you through this door is the Commander of the Faithful, the master of the Muslims and the seal of the Guardians (Wasi).”

In Tarikh Madinah-Damishq, (V.42, p. 303), Ibn Asaker has narrated this matter through a hadith from Anas in this manner: “O Anas! The first person who would enter through this door is the Commander of the Faithful, the honored leader of the radiant faces and the master of the believers, Ali (a.s.).” Also, refer to Kharazmi, Al-Manaqib, page 322-323.

Taftazani in Shahr al-Maqasid (V.5, p.259; the fourth discussion of the fourth chapter) has stated that the Prophet (s.a.w.a.) said, “Peace be upon him (i.e., upon Ali), leader of the believers”.