Is Isaiah a prophet from God, or was his mention a result of the distortion of the holy books?

The names of prophets and messengers are known only to Allah. Some of them have been mentioned in the Holy Qur'an, while others have not. Allah the Almighty says: ﴿And [We sent] messengers about whom We told you before, and messengers about whom We have not told you.﴾

The name "Isaiah" has been mentioned in books of exegesis with different spellings, such as "Asha'ya" or "Sha'ya." Exegetes mention him as one of the prophets of the Children of Israel whom the Children of Israel killed. However, mere mention does not indicate authenticity.

There is no mention of a prophet by this name in the Qur'an or the Sunnah. The narrations attributed to Ibn Abbas concerning him are weak in their chain of transmission, and even if they were authentic, they might be from what he received from the People of the Book, like Wahb ibn Munabbih, who used to transmit from them.

"Isaiah" is well-known among the People of the Book as a prophet, and there is a book named after him in the Old Testament.

There is no conclusive evidence to affirm or deny the prophethood of "Isaiah." What has been reported about him in books of exegesis is transmitted from the Children of Israel. The Prophet (peace be upon him) permitted narration from the Children of Israel without affirmation or denial. The Prophet (peace be upon him) said: «Convey from me even if it is a single verse, and narrate from the Children of Israel, there is no harm.» He also said: «When the People of the Book tell you something, do not believe them and do not disbelieve them.»

These Israelite narrations are mentioned for illustration, not for belief. They fall into three categories: what has been proven to be true, what has been proven to be false, and what has been left unspoken. The latter we neither believe nor disbelieve.