tend to offer little explanation, or interpret the in the hadith as love or support, or substitute with the word (of God, ). As such, Shias view the Ghadir Khumm as the investiture of Ali with Muhammad's religious and political authority, while Sunnis regard it as a statement about the rapport between the two men, or that Ali should execute Muhammad's will. On one occasion during his caliphate, Ali is known to have asked Muslims to come forward with their testimonies about the Ghadir Khumm. In doing so, McHugo suggests, Ali publicly claimed to have been entrusted by Muhammad with a spiritual and political authority greater than others, particularly his predecessors. The views of Madelung and Shah-Kazemi are similar. According to Lesley Hazleton, an author on religion and politics, Muhammad's statement at the Ghadir Khumm, "O God, befriend the friend of Ali and be the enemy of his enemy," was the standard formula for pledging allegiance in the Middle East at that time. Ali and his son Hasan both demanded a similar pledge of their supporters during their caliphates. The hadith of Ghadir Khumm is also cited by Ammar ibn Yasir, a companion of Ali, to support his right to the caliphate in the account of the Shia historian Ibn A'tham al-Kufi (ninth century) about the negotiations before the Battle of Siffin (657). This appears to be the earliest such instance in historical sources. Shia view For Shia Muslims, the Ghadir Khumm signifies the investiture of Ali with the guardianship () of the Muslim community after Muhammad. In particular, for them this was his most public announcement about the succession of Ali. Shia accounts describe how Umar and other companions visited Ali after the sermon to congratulate and pledge their allegiance to him, even addressing him as (). For Shias, the dramatic announcement at the Ghadir Khumm to thousands of Muslims in the heat of day hardly support its Sunni interpretation of love () and support () for Ali. These two are the obligations of every Muslim towards other Muslims, not just Ali, thus weakening the Sunni interpretation again. Alternatively, the Sunni Ibn Kathir () considers the Ghadir Khumm a response to the complaints about Ali during his expedition to Yemen, while the Shia Ibn Shahrashub () counters that Muhammad had already dismissed those objections, "Do not complain about Ali, for he is sternly scrupulous only for the sake of