What is the authenticity of the narration about the deer and the Jew attributed to the Prophet, may Allah bless him and grant him peace?

If the questioner is referring to the Hadith (definition) of the wolf that came to the shepherd, this Hadith was narrated by Ahmad, and its chain of transmission was authenticated by Al-Suyuti and Al-Qastalani. Its summary is that a wolf took a sheep from a shepherd, and the shepherd retrieved it. The wolf then spoke, reproaching him. The shepherd was astonished, so the wolf told him something even more astonishing, which was the existence of a man—the Prophet, peace and blessings be upon him—who informs about what has passed and what is to come. So, the man embraced Islam, and the Prophet, peace and blessings be upon him, affirmed his truthfulness and said: "This is a sign from among the signs preceding the Hour."