That morning, the sun of hearts rose from Hara .... .

The Prophet Mohammad (PBUH&HP) used to spend private times alone and many times with Ali son of Abi-Taleb, on Hara to worship the Lord. But that day, Rajab the twenty seventh, year 13 B.H., it was different; the angel Gabriel with seventy thousand angels accompanying him and the angel Michael with seventy thousand angels accompanying him, came to Mohammad; everywhere Mohammad looked, there were angels; the Message of Allah was delivered to Mohammad -the most beloved and exalted creation of Allah- and he started his Divine Mission on earth ... .
As the prophet Mohammad (PBUH&HP)descended the mountain, his face was light-full from the light of Allah; every tree, plant and stone which he passed by, clearly greeted him and said:
Salaam be upon you, the Prophet of Allah; Salaam be upon you, the Messenger of Allah ... .
(Montahi-Ol-Amaal,...)
It is not only the Shia'h who believe that Ali(PBUH) was the first one believing in the Prophet Mohammad ;
The Prophet Mohammad (PBUH&HP) has said:
O' Ali ! In the matter of Prophet-hood, I have superiority over you and you have superiority over other people in seven matters and no one from Qoraish can ever stand against you: you are the first person who believed in Allah; you are the most faithful to the Covenant of Allah; you are the firmest and most confirmed regarding the Amr of Allah; you are the most deserving to divide equally; you are the fairest to the people; you are the most insightful and knowledgeable in judging;, regarding advantages, you are the most honored by Allah .
(Sunni document:Kanz-Omaal, History of Damascus, Ebne-Asaaker, Manaqeb, Kharazmi, Yanabi-Ol-Mawaddah,...)

Eid of Mab'ath MOBARAK