Amongst the companions of the Prophet (s), Imam Ali (a) was the one who left a very rich heritage of morality and spirituality, so much so that no one who has knowledge of the early days of Islam and the companions of the Prophet (s) would have any doubt that amongst the followers and companions of the Prophet (s), Imam Ali (a) was the most knowledgeable as well as the most spiritual.
This is not only evident in Shi’a Islam but also in Sufi Islam. The majority of Sufis are not Shi’a but nevertheless they all believe that their genealogy goes back to the Imams of the Ahl al-Bayt (a), finally arriving at Imam Ali (a), and then through Imam Ali (a) they connect themselves to the Prophet (s). It is very rare to find a Sufi order which does not trace its genealogy back to Imam Ali (a).
In any case, there is no doubt that in his way of life and in his words, Imam Ali (a) represented the teachings of the Prophet (s) more than anyone else from amongst the companions of the Prophet (s). To understand this, it is sufficient simply to study Nahj al-Balāghah, which is a collection of sermons, letters, and wise sayings containing only a fraction of all the sayings of Imam Ali (a). There are also many other books available such as Ghurar al-Hikam and ‘Uyūn al-Hikam wa al-Mawa‘idh in which many wise moral sayings of Imam Ali (a) can be found.
In Nahj al-Balāghah we find such important questions and teachings on morality – in addition to philosophical and theological issues – that any serious reader would be very much encouraged to undertake a study of ethics. It is impossible to read Nahj al-Balāghah carefully and not be inspired to take morality seriously. Indeed, after reading it, one realises that one’s whole life depends on taking morality seriously.
For example, in one of Imam Ali’s letters addressed to his son, Imam al-Hasan (a), the Imam (a) gives such important moral advice that several books and commentaries have been written on this letter alone. Indeed, a Sunni scholar named Abu Ahmad Hasan b. ‘Abdillah quotes this letter in his book al-Zawājir wa al-Mawāiż and says that if there is one piece of advice that needs to be written in gold, it is this letter of Imam Ali (a) to Imam al-Hasan (s). Of course, this is just one example amongst many others.