156. Amīr al-mu’minīn, peace be upon him, said: On you lies (the obligation of) obedience to the person about whom you cannot plead the excuse of ignorance. 
 Just as Allāh sent down a series of prophets by way of His Justice and Mercy to guide and direct towards religion, in the same way He laid down the system of the Imāmate to protect religion from alteration and change so that every Imām may in his time save the Divine teachings from the onslaught of personal desires and give directions about the correct precepts of Islam. And just as it is obligatory to know the originator of the religion (i.e., the Prophet) in the same way it is necessary to know the protector of the religion; and he who remains ignorant of him cannot be excused because the issue of Imāmate is supported by so many proofs and testimonies that no intelligent person can find any way to deny it. Thus, the Holy Prophet has said:
Whoever dies without knowing the Imām of his time dies a pre-Islamic (jāhiliyyah) death. (Sharḥ al-maqāṣid, at-Taftāzānī ash-Shāfi‘ī, vol. 2, p. 275; al-Jawāhir al-muḍiyyah, al-Khaṭīb al-Ḥanafī, vol .2, pp. 457, 509).
It has also been narrated by ‘Abdullāh ibn ‘Umar, Mu‘āwiyah ibn Abī Sufyān and ‘Abdullāh ibn al-‘Abbās that the Messenger of Allāh, peace be upon him and his descendants, said that:
One who dies without (knowing his) Imām and binding himself by an oath of allegiance to him will die the death of one belonging to the days of jāhiliyyah, and one who withdraws his hand from obedience (to the Imām) will find no argument (in his defence) when he stands before
Allāh on the Day of Judgement. (al-Musnad, aṭ-Ṭayālisī, p. 259; aṣ-Ṣaḥīḥ, Muslim, vol. 6, p. 22; al-Musnad, Aḥmad ibn Ḥanbal, vol. 4, p. 96; as-Sunan al-kubrā, al-Bayhaqī, vol. 8, p. 156; at-Tafsīr, Ibn Kathīr, vol. 1, p. 517; Majma‘ az-zawā’id, vol. 5, pp. 218, 224, 225)
Ibn Abi’l-Ḥadīd also agrees that the personality about whom no one’s ignorance can be excused is that of Amīr al-mu’minīn. He also acknowledges the obligation to obey him and holds that he who does not believe in the issue of Imāmate will not achieve deliverance. In this connection he writes:
He who is ignorant of the position of ‘Alī, peace be upon him, as Imām and denies its veracity or obligatory character would, according to our associates, remain in Hell for ever, his fasting or prayers being of no avail to him, because the knowledge of this matter is among the basic principles which constitute the foundations of religion. However, we do not regard one who denies his Imāmate as an unbeliever but only a sinner, a transgressor or a deviator, etc. (Sharḥ Nahj al-balāghah, vol. 18, p. 373)