Sahih Bukhari Volume 008, Book 074, Hadith Number 282.
Narated By 'Abdullah bin 'Abbas : 'Ali bin Abu Talib came out of the house of the Prophet during his fatal ailment. The people asked ('Ali), "O Abu Hasan! How is the health of Allah's Apostle this morning?" 'Ali said, "This morning he is better, with the grace of Allah." Al-'Abbas held Ali by the hand and said, "Don't you see him (about to die)? By Allah, within three days you will be the slave of the stick (i.e., under the command of another ruler). By Allah, I think that Allah's Apostle will die from his present ailment, for I know the signs of death on the faces of the offspring of 'Abdul Muttalib. So let us go to Allah's Apostle to ask him who will take over the Caliphate. If the authority is given to us, we will know it, and if it is given to somebody else we will request him to recommend us to him. " 'Ali said, "By Allah! If we ask Allah's Apostle for the ruler ship and he refuses, then the people will never give it to us. Besides, I will never ask Allah's Apostle for it." (See Hadith No.728, Vol.5)