What is the authenticity of the narration about the boy who spoke on the day of his birth, saying to the Prophet, peace and blessings be upon him, "You are the Messenger of Allah," what is the ruling of scholars on it, and has any of them authenticated it?

This Hadith is not authentic. It was narrated by Al-Bayhaqi, Al-Khatib al-Baghdadi, and others. Al-Sam'ani said: "Most of its chains of narration are weak," and Al-Bayhaqi said: "If the narration concerning it is authentic," which indicates that he did not authenticate it. Ibn Kathir said: "It is a very strange Hadith" due to the possibility of its weakness in the text or chain of narration. People have spoken about Muhammad ibn Yunus al-Kudaymi (one of its narrators) and accused him of fabricating Hadith and lying, and many شيخs (scholars) abandoned narrating from him. It was said that he fabricated more than a thousand Hadith. Although a boy speaking is not intellectually or legally objectionable, as it occurred in the story of Jurayj the worshipper, this does not authenticate the Hadith. This Hadith was narrated with another chain of narration, which is good (hasan), but its text contradicts the first narration.