Sunan Abi Dawud Book 42, Hadith 36
The Caliphs are five: Abu Bakr, ‘Umar, ‘Uthman, ‘All and ‘Umar b. ‘Abd al-Aziz.
I heard Sufyan say: If anyone thinks that ‘All (Allah be pleased with him) was more deserving for the Caliphate than both of them, he imputed error to Abu Bakr, ‘Umar, the Muhajirun (Immigrants), and the Ansar (Helpers) Allah be pleased with all of them. I think that with this (belief) none of his action will rise to the heaven.
Abu Hurairah said that a man came to the Messenger of Allah (ﷺ) and said: I saw (in my dream) a piece of cloud from which ghee and honey were dropping. I saw the people spreading their hands. Some of them took much and some a little. I also saw a rope hanging from Heaven to Earth. I saw, Messenger of Allah, that you caught hold of it and ascended by it. Then another man caught hold of it and ascended it. Then another man caught hold of it and ascended it. Then another man caught hold of it, but it broke, and then it was joined and he ascended it.
AbuBakr said: May my parents be sacrificed for you, if you allow, I shall interpret it.
He said: Interpret it. He said: The piece of cloud is the cloud of Islam; the ghee and honey that were dropping from it are the Qur'an, which contains softness and sweetness. Those who received much or little of it are those who learn much or little of the Qur'an. The rope hanging from Heaven to Earth is the truth which you are following. You catch hold of it and then Allah will raise you to Him. Then another man will catch hold of it and ascend it, Then another man will catch hold of it and it will break. But it will be joined and he will ascend it. Tell me. Messenger of Allah, whether I am right or wrong.
He said: You are partly right and partly wrong. He said: I adjure you by Allah, you should tell me where I am wrong.
The Prophet (ﷺ) said: Do not take an oath.