What is the difference between understanding the authenticity of a Hadith directly from its chain of narration (isnad) in Bukhari or Muslim, and the need for other Hadith scholars to authenticate it? And how is the authenticity of Hadiths understood when they appear in books of Tafsir (exegesis) where it suffices to state "Narrated by so-and-so" without mentioning the Hadith's classification?

Among the books of Hadith, some authors committed themselves to authenticity, while others did not. Scholars evaluate these Hadith books according to the rules of Hadith science. As for the books of Tafsir (exegesis), what is presented in them combines authentic, weak, fabricated, and Isra'iliyyat (narratives of Jewish origin). The phrase "narrated by so-and-so" does not imply the authenticity of the Hadith; rather, one must examine the chain of narration (isnad) and the text (matn). The exegeses of the Companions and the Tabi'in (successors) include authentic, good, weak, fabricated, and Isra'iliyyat narratives. Imam Ahmad said: "Three things have no origin: Tafsir, Malahim (apocalyptic battles), and Maghazi (military expeditions)." His intention was that most of these lack authentic chains of narration. It is recommended to consult the books "Al-Isra'iliyyat wal-Mawdu'at fi Kutub al-Tafsir" by Abu Shahbah, and "Al-Tafsir wal-Mufassirun" by Al-Dhahabi, as well as books on graduating (authenticating) Hadith of Tafsir, such as "Al-Kafi al-Shafi fi Takhrij Ahadith al-Kashshaf" by Ibn Hajar.