Prophets are infallible from all minor and major sins;

One logical reasoning to accept this is that if one believes the Ambiyāʾ can sin, it would also entail the possibility of lying, which is impossible. Anything attributed to a Prophet that could affect the authenticity of the message is rejected.

Human beings are divided into two groups: the infallible and the fallible. The infallible are the Messengers, while the fallible are the rest of creation.

Now let us look in regard to the incident of Sayyidunā Ādam (peace be upon him) eating from the tree.

Some people, who lack knowledge, wrongfully deem that it was the fault of Sayyidunā Ādam (peace be upon him) that drove us out of Jannah, and that if this had not happened, we would still be there today. This statement is illogical and textually incorrect because Allāh, the Almighty, before the creation of Nabī Ādam, said to the Malāʾikah (angels): ‘Indeed, I will make upon the earth a Khalīfah.’

So Prophet Ādam (peace be upon him) did not commit a sin for a number of reasons firstly it was out of forgetfulness, secondly it was already all pre-ordained to happen as mentioned in the Qurʾān and narrations before the creation of Nabī Ādam:

“And when your Lord said to the angels, ‘Indeed, I will make upon the earth a Khalīfah."' [2:30]

This was said before the creation of Sayyidunā Ādam to the Malāʾikah, it was already ordained by Allāh for Ādam (peace be upon him) to be sent to the earth for there to be a Khalīfah established in earth. So Nabī Ādam did not commit a sin in eating from the tree, rather it was ordained for the established plan of Allāh in this verse.

The fall of Prophet Ādam (peace be upon him) to Earth was not a way to insult. Rather, it was the fall of dignity and not something of disgrace, as mentioned by those who know Allāh greatness. Allah Almighty knew that our father Ādam and mother Ḥawwāʾ (peace be upon them) would eat from the tree and that they would go down to the Earth. As for their experience of dwelling in Heaven this was required as they were made to be sent as pillars of the Khilāfah on Earth. So for this Nabī Adam and Ḥawwāʾ had to know their species and know the reality of the rejected Shayṭān that made them expelled from Heaven, so that the command is once and for all established that the path that leads to Heaven is only through the obedience to Allāh and knowing the enmity of the cursed Shayṭān:

The prohibition that was mentioned by Allāh of not going near that tree and eating its fruit was an advisory command and not a legislative command. So to go against that it is not recommended but would not be considered a sin but rather a action that will lead to unwanted consequences if the contrary is done to it. So in the case of Sayyidunā Ādam and Sayyidatunā Ḥawwāʾ the result and consequences they faced was their cancellation of their tenure as guests of Allāh in the Paradise and its comforts. A word which is mentioned in relation to Ādam (peace be upon him) in Sūrah Ṭā-Hā verse 121 and the meaning taken for the word عَصَى which is "disobeyed" the advisory command but will not be considered a sin.

To look at another word in the same verse which is غَوَى “he erred” as to say leaving the more appropriate and better behaviour to something that is less preferred which will result in unwanted consequences. So Ādam (peace be upon him) erring does not make him guilty of committing a sin but rather being told he erred in not choosing the better action that was advised to him. 

One must also know a Arabic word can have multiple meaning and does not always have just one restricted meaning. Let us look at some of these words the first being mentioned in Sūrah al-Baqarah verse 35 "الظالمين" this verse in itself has a few meanings to mention a few:

1) To Misplace something 

2) To oppress

3) To make something occur more faster

4) To get harmed

Meanings 3 and 4 are the most suitable and align with the event at hand. If it were to mean something faster, it would suggest they were destined to go to Earth, but eating from the tree hastened their departure to Earth earlier than the intended time. The next meaning refers to getting harmed, which means facing the difficulties of worldly life by losing the comforts of heaven.

Then in another verse it states Ādam was already told that this will occur but forgot فَنَسِىَ and when he ate from the tree it was out of forgetfulness and not a sin:

“And We had already taken a promise from Adam before, but he forgot; and We found not in him determination.” [Sūrah Ṭā-Hā, verse 115]

The great Mufassirīn and others also mention that it was not a sin, as the Prophets are infallible and do not intend to sin nor commit sin. They are more fearful of Allāh and are protected from sin.

► Tafsīr al-Ṭabarānī under Sūrah Ṭā-Hā Verse 121

 أجاب قوم عن الكلام الأول فقالوا: المعصية مخالفة الأمر، والأمر قد يكون بالواجب والندب فإنهم يقولون: أشرت عليه في أمر ولده في كذا فعصاني، وأمرته بشرب الدواء فعصاني، وإذا كان الأمر كذلك لم يمتنع إطلاق اسم العصيان على آدم لا لكونه تاركاً للواجب بل لكونه تاركاً للمندوب.

A anecdote is mentioned to further understand this:

If one were to say, for example, to someone to drink medicine, and the person disobeys by not drinking the medicine for their illness, it would not make them a sinner but rather disobedient for not doing something that would have been better and more beneficial for their health.

Similarly, the case of Ādam (peace be upon him) was such that he was called disobedient not because he committed a sin, but rather because he did not do something he was told to do—i.e., not eating from the tree, which would have been better for him to avoid.

► Tafsīr al-Rāzī by Imām Fakhr al-Dīn al-Rāzī under Sūrah Ṭā-Hā, Verse 121.

Then later on after Nabī Ādam veiled from the worldly life, he explained again that it was not his fault and not a sin rather it was all ordained by Allāh forty years before his creation for all this to occur:

Narrated by Sayyidunā Abū Hurayra:

The Prophet ‎ﷺ said, "Ādam and Mūsā argued with each other. Moses said to Ādam. 'O Ādam! You are our father who disappointed us and turned us out of Paradise.' Then Ādam said to him, 'O Mūsā! Allāh favoured you with His talk (talked to you directly) and He wrote (the Tawrāh) for you with his Hand (Bilā Kayf). Do you blame me for action which Allāh had written in my fate forty years before my creation?' So Ādam confuted Mūsā, Ādam confuted Mūsā," the Prophet ‎ﷺ added, repeating the Statement three times.

[Ṣaḥīḥ al-Bukhārī 6614, 3409]

Sayyidunā Ādam (peace be upon him) also clarifies all this himself and also establishes the fact that the reason even Nabī Mūsā (peace be upon him) was blessed with his speech with Allāh was because of Ādam being sent to the earth which allowed this to happen for Mūsā. Another point of interest is the fact both Prophets are talking to each other after their passing from this world also profess the belief that the Prophets are alive and are free to do as they wish such as communicating with other Anbiyāʾ.

To conclude with a verse of the holy Qurʾān proving once and for all the high esteem and honour Allāh mentions for Sayyidunā Ādam:

"Indeed, Allāh chose Ādam and Nūḥ and the family of Ibrāhīm and the family of ʿImrān over the worlds."

[Sūrah Āli ʿImrān, verse 33]

Credit: Clarifying Lights