How can one tell if a story mentioned in the book "Tarikh al-Tabari" is from the Israʼiliyyat?

Isra'iliyyat can be identified as narratives originating from the Jews and Christians, or tales of past peoples not mentioned by Allah in the Quran or by the Prophet, peace be upon him, in the Sunnah (definition). What Allah has narrated or what is found in authentic Hadith (definition) is not Isra'iliyyat; rather, it is revelation. As for stories not found in the Quran or authentic Hadith, they are dealt with according to the Hadith: "When the People of the Book narrate to you, do not believe them nor disbelieve them, but say: 'We believe in Allah and His messengers,' for if it was false, you would not have believed it, and if it was true, you would not have disbelieved it."