Imam Ali (a) passed the following instructions to his family a little before his martyrdom.
My advice to you is that you should not consider anyone as a co-worker of the Lord, be firm in your belief that there is One and only One Allah. Do not waste the knowledge given to you by the Holy Prophet (s) and do not give up and destroy his Sunnah (traditions). Keep these two pillars of Islam (monotheism and Sunnah of the Holy Prophet (s)) aloft. If you act according to my advice then you cannot be blamed for damaging or destroying the religion.
Until yesterday I was your Amir, today I am only an object from whom you can take lesson and warnings, and tomorrow I shall part company with you. If I survive this fatal wound I shall be at liberty to decide how to treat the man who attempted to kill me. If I die then my worldly life comes to an end. If I forgive my assassin then it will be to gain the Blessings of Allah for forgiving a person who has harmed you, and it will be a good deed if you also forgive him. Do you not desire to be forgiven by the Lord? I swear by Allah that death is not coming to me suddenly and unexpectedly that I may hate or abhor, neither is it such a visitor whom I may refuse to meet. So far as death by martyrdom is concerned I always expected and desired it and I now welcome it like a thirsty person who finds water when he is extremely thirsty. I am a seeker whom martyrdom finds what he was seeking for. To the pious people the best is that which they find with Allah.