Revelation of Verse on Protection in Mecca
Suyuti[1] quotes Ibn Abbas as saying that they asked the Prophet (PBUH): Which verse became onerous to you? He replied: "During Hajj pilgrimage in Mena, where the Arab infidels and other people were also there, Gabriel came to me and said: "O Messenger, announce that which has been revealed to you ..." I stood up and said: O, people, who will help me to deliver the Message of Allah to enter the Heaven. People! Say "There is no God but Allah" and Muhammad is the Messenger of Allah to enjoy salvation and to enter the Heaven. Then everyone from young and old, men and women attacked me with dust and rock calling me a liar. Then my uncle Abbas came and saved my life.[2]
And Shia response to this confusion is:
This is a hadith forged by Bani Abbas to gain superiority for themselves against Alavids since, first, the verse (announce that which has been revealed to you) was not sent for Shias and Sunnis in early years after prophetic mission. There is no reason for repeating the cause of revelation, i.e. to say it has been sent twice but expressed in the second revelation.
Third, this hadith is a single tradition that opposes all other similar traditions, so it shall be put aside as an unreliable hadith.
source : www.tebyan.net