According to Imam Ali a.s in nahjul balagha, for guidance Prophet s.a.w.w left behind the Quran (Book of Allah) only. Exactly what is mentioned in hadith e saqlain as narrated by other companions. http://www.sunnah.com/muslim/44/55
Nahjul Balagha Sermon #1 https://www.al-islam.org/nahjul-balagha-part-1-sermons/sermon-1-praise-due-Allah-whose-worth-cannot-be-described
In this sermon Imam Ali a.s addressed many core and fundamental principles of Islam but said nothing about divine imamate or wilayah of ahlebayt. He also didnt mention that the Prophet s.a.w.w left behind the Quran and Ahlul-Bayt as guidance, only the Quran and this was the way of previous Prophets.
Allah chooses His Prophets
From his (Adam’s) progeny Allah chose prophets and took their pledge for his revelation and for carrying His message as their trust. In course of time many people perverted Allah’s trust with them and ignored His position and took compeers along with Him. Satan turned them away from knowing Him and kept them aloof from His worship. Then Allah sent His Messengers and series of His prophets towards them to get them to fulfil the pledges of His creation, to recall to them His bounties, to exhort them by preaching, to unveil before them the hidden virtues of wisdom and show them the signs of His Omnipotence namely the sky which is raised over them, the earth that is placed beneath them, means of living that sustain them, deaths that make them die, ailments that turn them old and incidents that successively betake them.
Allah never allowed His creation to remain without a Prophet deputised by Him, or a book sent down from Him or a binding argument or a standing plea. These Messengers were such that they did not feel little because of smallness of their number or of largeness of the number of their falsifiers. Among them was either a predecessor who would name the one to follow or the follower who had been introduced by the predecessor.
The Prophethood of Muhammad s.a.w.w
In this way ages passed by and times rolled on, fathers passed away while sons took their places till Allah deputised Muhammad (peace be upon him and his progeny) as His Prophet, in fulfilment of His promise and in completion of His Prophethood. His pledge had been taken from the Prophets, his traits of character were well reputed and his birth was honourable. The people of the earth at this time were divided in different parties, their aims were separate and ways were diverse. They either likened Allah with His creation or twisted His Names or turned to else than Him. Through Muhammad (S) Allah guided them out of wrong and with his efforts took them out of ignorance.
Then Allah chose for Muhammad, peace be upon him and on his progeny, to meet Him, selected him for His own nearness, regarded him too dignified to remain in this world and decided to remove him from this place of trial. So He drew him towards Himself with honour. Allah may shower His blessing on him, and his progeny.
The Holy Qur’an and Sunnah
But the Prophet left among you the same which other Prophets left among their peoples, because Prophets do not leave them untended (in dark) without a clear path and a standing ensign, namely the Book of your Creator clarifying its permission and prohibitions, its obligations and discretion, its repealing injunctions and the repealed ones, its permissible matters and compulsory ones, its particulars and the general ones, its lessons and illustrations, its long and the short ones, its clear and obscure ones, detailing its abbreviations and clarifying its obscurities.
In it there are some verses whose knowledge is obligatory and others whose ignorance by the people is permissible. It also contains what appears to be obligatory according to the Book but its repeal is signified by the Prophet’s action (sunnah) or that which appears compulsory according to the Prophet’s action but the Book allows not following it.
Or there are those which are obligatory in a given time but not so after that time. Its prohibitions also differ. Some are major regarding which there exists the threat of fire (Hell), and others are minor for which there are prospects of forgiveness. There are also those of which a small portion is also acceptable (to Allah) but they are capable of being expanded.
Jazak Allah Khairan