Three days later, after refusing to join the dispatch of Usama, was when that mournful day came and the Quraysh group was ready. As the Prophet was on his deathbed, they made their most decisive move that would ensure their transitory success – a shift that would eventually divert the course of Islamic history forever. This act later became known as the “Calamity of Thursday.” This event is recorded in Sahih al-Bukhari, which is considered to be the most authentic book after the Holy Qur’an in the Sunni tradition.
Gravely ill, and surrounded by some of the companions, the Prophet requested a pen and paper to narrate his will, a hadith he said that would guard the nation from misguidance. Sensing that the Prophet again wanted to name his successor (Ali b. Abi Talib) one last time, the companion, Umar b. al-Khattab spearheaded the Quraysh group by interceding and declaring, “We have the book of Allah, and it suffices for us.” He then accused the Prophet of Islam of hallucinating (yahjor) because of his illness. An argument ensued over Umar’s comment and the Prophet angrily requested them to leave. & 
The power ambition was too much to let pass, because long afterwards and during his reign, Umar b. al-Khattab said regarding that day, “I knew the Prophet was going to mention the name of Ali as his successor, so I objected to that and refused.”
After challenging the will of the Prophet, it is not surprising to witness centuries of unsettling political and ideological differences within the ummah. Perhaps, during the eras of the first four caliphs, Islam was still a spiritually inclined faith and united and bonded by primarily one following – one ummah – but the aspirations of some permitted the way of division. The institute of the khalifah was reduced to a mere political acquisition and many Muslims began their slow turn away from what Islam had intended. Corruption and greed earmarked the powerhouses of government and institutes that later sprung up during the Bani Umayyah and Bani Abbas dynasties. It can be said that the era of corruption by these dynasties had been intricately connected to the “Calamity of Thursday.”
 The Messenger of God said, “Bring me a tablet (lawh) and an inkpot (dawat), so that I can write for you a document, after which you will not go astray.” A person said that the Messenger of God was talking “deliriously.” Tarikh al-Tabari, Vol. 9 translated by Ismail. K. Poonawala p. 175.
 In the older Sahih al-Bukhari books, the term “yahjor” can be found, but in the latest versions, the hadith has been modified as, “that the Prophet has been overwhelmed by pain.”
 Sahih al-Bukhari, Kitab al-Jihad wal-Seer, 2:118; Sahih al-Muslim; Ithbat al-Wasyah; Musnad Ahmad, 3:346
 For full details read Inquiries about Shia Islam by the same author.
 Ibn Abil Hadid, Sharh Nahjul-Balaghah, 3:114