Infallibility is the inability to be wrong. Its importance and meaning is debated in epistemology and major religions.
The five Ineffable greatest personalities (The Prophet (SAWA), Imam Ali (AS), Fatima (AS), Imam Hasan (AS) and Imam Husain (AS) have repeatedly said in many authentic Hadeeths that all the nine following Imams are Infallible. Believing in Hadeeth al-Kisa leads definitely to believing that what ever was said by the greatest Five is the absolute truth which is strong evidence that all the twelve Imams are Infallible.
The great status of Sayyeda Zaynab (SA) and Hazrat Abbas (AS) is above our thinking, that is why we can not determine their level of Ismah. It is known to Allah (SWT), the Prophet (SAWA) and Ahlul Bayt (AS).
All the Prophets are Infallibles with no exception at all.
The status of the fourteen Infallables ( Muhammad , Ali, Fatimah, Hasan, Husain and nine Imams from Imam Husain) is The highest above all noble human beings. No doubt there are very pious personalities like Lady Maryam Bint Imran and Lady Asiya Bint Muzahim who have got a degree of infallibility which is called by some scholars as minor infallibility. Minor infallibility means a high state of piousness in which the person keeps himself away from sins because of continuous remembering Allah (SWT). This type of infallibility is less than the infallibility of the 14 Ma'soomeen (AS).
Lady Zaynab (AS) and Hazrat Abbas (AS) were best of the best pious people but their status is after the status of the 14 Ma'soomeen. Many scholars call their infallibility as acquired infallibility which is a result of highest degrees of Taqwa and piousness.
In the book Aqaed al-Haqqa by Ayatullah Sayed Ali Sadr we find infallibility categorized into 3 levels:
1. Ismat ul Kubra which is reserved for the 14 Infallibles. They do not commit sins, mistakes or even tark al-awla (choosing the less preferred method). We as Shia however do not believe that any of the prophets, from their birth until their death, committed any sins at all whether big or small. We see that the honorable Shia scholar, Sheikh Mufid stated that the prophets and Imams never committed sins or even left the recommended actions (mustahab) and that they were perfect in every aspect of their lives.
Another point to bring is that the prophets are not infallible by force. Rather, they are infallible by utilizing their intellectual ability to not succumb to sin. They have the ability to sin, but they choose not to sin. They know the effects and evil disgusting nature of sin and are repulsed by it. An example would be, if we saw an old piece of food that was rotten would we eat that food? Of course not! It is repulsive to us because we see its rottenness. This is how the prophets see sin. They see the rottenness in disobeying God, whereas most of mankind is attracted to the sins because they have been made fair-seeming to them.
2. Ismat ul-Ithbaatiya which is for the general prophets where they do not commit sins, but it is possible for them to do tark al-awla (choosing the less preferred method).
3. Ismat ul- Thubutiya which is an acquired level of infallibility by abandoning sins and continuously doing their responsibilities to Allah and are obedient to Him. They are just individuals and are far away from deviation. We find this type of acquired infallibility in some of the progeny of the infallibles such as Zaynab, Abbas and Masuma (as) and others.
The Infallible Imam has the maximum knowledge which is continuation of the knowledge of the Prophet (SAWA) which is from Allah , and has the absolute obedience of Allah (SWT) in each and every act he does and word he alters. Infallible Imam can never be away from the Twelve Imams mentioned by the Prophet Muhammad (SAWA).
Yes, every prophet had a successor who leads his Ummah after the Prophet and all of them are infallible. The Hadeeth لكل نبي وصي is narrated in Shia and Sunni books. Among Sunni scholars who narrated this Hadeeth are Ibn Hanbal in Fadha'l al-Sahabah, Sibt Ibn al-Jawzi in Tathkirat al-Khawaass, Ibn al-Maghaazili in al-Manaaqib, al-Tabaraani in al-Mo'jam al-Kabeer and Ibn Asaakir in Tareekh Dimishq and many others.
The fact of the infallibility of Ameerul Mo'mineen and other 11 Imams was known to the believers during the lives of the Infallible, and nothing emerged later in hindsight.
All the prophets and their divine successors are infallible and sinless as they are the best examples to be followed by human beings. Allah (SWT) ordered all human beings to obey the prophets and their successors. If God forbid, they do any sinful act, it means that Allah (SWT) is ordering us to commit sin following them, which is impossible.
Sura al-Nasr like many other Surah have been mistranslated. It does mean at all to seek forgiveness for the prophet himself but for the Muslims who enter in the Religion of Allah for their past sins.
Every verse in Quran and every Hadeeth on this matter means that the Prophet is seeking forgiveness for the Believers.
Thank you for your question. Each person's reward is in accordance with the tests they face in relation to the gifts and abilities they have been given. As such people who are not born infallible will not be judged in the same way that the Infallibles (as) are. But at the same time, they are also not tested with the responsibilities of the Infallibles (as), nor are they rewarded in the same way. Infallibility is a knowledge that keeps a person away from sin and mistakes. It does not remove the free choice and therefore does not negate the applicability of reward for great actions.
May you always be successful
The Prophet (SAWA) did not pray to Allah to keep Ahlul Bayt (AS) away from Rijs, but he prayed to Allah to keep the Rijs away from Ahlul Bayt (AS).
This is a misunderstanding in the minds of many who do not realize the difference between (A'nhom) عنهم , and (Minhom) منهم or error in the translation.
A'anhom: means to drive the bad away not to be near them.
Minhom : means to drive the bad from them.
Allah (SWT) never said Minhom, but said A'nhom.
انما يريد الله ليذهب عنكم الرجس أهل البيت ويطهركم تطهيرا (33:33)
Ahlul Bayt (AS) are The Infallible Divine leaders who are completely purified by Allah (SWT) who stated in Quran that He wants to to keep the bad away from them because they have nothing from the bad at all.
It is Not correct at all to claim that the Prophet Muhammad (SAWA) was the least imperfect human.
There is not a single evidence about any imperfectness is the life of Prophet (SAWA).
The Prophet Muhammad (SAWA) is the Most Perfect Human and The best of All the Prophets.
The meanings of Quranic verses must be taken from the Prophet himself as Allah (SWT) said in Quran وأنزلنا إليك الذكر لتبين للناس ما نزل إليهم
( We revealed on you the Thikr ( full knowledge of Quran) So that you explain to the people what was revealed for them). Al-Nahl, 44)
Verses which seem to suggest that any Prophet was fallible, are been misunderstood. Verses regarding Prophet Adam (AS) are been explained by the Prophet Muhammad (SAWA) and his Holy Progeny confirming that Adam did not commit any sin whatsoever.
Ahlul Bayt (AS) had many debates in this subject including a very well known debate between Imam Al-Redha (AS) and Al-Ma’moon al-Abbasi, the ruler of that time, in which al-Ma’moon put to the Imam ( AS) the Quranic verses which were according his understanding, showing fallibility of some prophets, and Imam Al-Redha (AS) explained the real meaning which confirms infallibility of all the Prophets.
You may see Tanzeeh al- Anbiyaa’ by al-Shaikh al- Mofeed. تنزيه الأنبياء للشيخ النفيد.
The claim of fallibility of any Prophet goes against Quran where Allah orders people to absolutely obey the prophets. Allah will never order people to obey a sinner.