Ghadir is an undeniable fact in the history of Islam and will never be forgotten. Therefore, Imam Ali (A. S.) from the first days of Abu-Bakr’s caliphate in addition to counting the excellences made him entitled to caliphate referred to the narration of Ghadir. His action in telling the event of Ghadir and recounting of it was in fact challenging the rule of the usurpators of the caliphate. Imam performed this action both in confronting Abu Bakr and then at the time of next caliphs. He referred to the event of Ghadir and his nomination by the Holy Prophet for the Islamic caliphate even after undertaking the position. His reasoning by the narration of Ghadir is discussed in this article.