Why are there scholars who classedfied Some hadiths in Sahih al bukhari and Sahih Muslim as weak while the majoraty of the muslims and scholars where certen that all hadiths in Sahih al bukhari and in Sahih Muslim are authentic.And I heard that albani and Ibn baz and Ibn Utheymien Said that ther are Some weak hadiths is that true?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is no doubt that Saheeh Al-Bukhari and Saheeh Muslim are the most authentic Hadith collections, and the Muslim nation received them with full acceptance.

Imam An-Nawawi said in his book Sharh Saheeh Muslim:

“The Muslim scholars agreed upon the fact that Saheeh Al-Bukhari and Saheeh Muslim are the most authentic books after the Quran, and the Muslim Ummah received them with full acceptance. Saheeh Al-Bukhari is more authentic and abounds in greater benefits and knowledge than Saheeh Muslim.” [End of quote]

This means that the general majority of the Hadiths recorded in Saheeh Al-Bukhari and Saheeh Muslim are authentic and have been accepted by the Ummah, but there are few Hadiths therein that were criticized by some senior Hadith scholars, such as Imam Ad-Daraqutni . However, this does not undermine nor discredit their two books in their totality because the criticized Hadiths are few in number and their chains of narrations included some narrators who were classified by Hadith scholars as slightly weak.

In refutation, the scholars underlined that Al-Bukhari and Muslim chose the authentic Hadiths narrated by these reporters with weak memorization skills from the ones that were known to be authentic. Al-Hafith Ibn Hajar allocated a chapter in the introduction of his book Sharh Saheeh Al-Bukhari in which he compiled the hadiths that were criticized by Al-Hafith Ad-Daraqutni and other critics. He listed these Hadith and also allocated a chapter for the names of the narrators accepted by Al-Bukhari who were criticized by other scholars and refuted their criticism.

The contemporary scholars who judged some Hadiths recorded in Saheeh Al-Bukhari inauthentic based on their personal reasoning, and other senior scholars like Al-Hafith Ad-Daraqutni.

As what you mentioned about Shaykh Ibn Baz he was asked about his opinion on those who classified the Hadiths recorded in Saheeh Muslim or Saheeh Al-Bukhari as inauthentic.

He replied, “This is an odd opinion that deviates from that of the Hadith scholars and is not acceptable except in very few narrations recorded by Muslim as pointed out by Ad-Daraqutni and others. The majority of scholars held that the Hadith recorded in Saheeh Al-Bukhari and Saheeh Muslim were received with full acceptance and adducible as evidence (to be used as valid arguments) as stated by Al-Hafith Ibn Hajar, Al-Hafith Ibn As-Salah, and others. If some narrators whose narrations were recorded in Saheeh Al-Bukhari and Saheeh Muslim were weak, they chose their acceptable narrations. Examples of these reporters were Isma‘eel ibn Abu Uways, ‘Umar ibn Hamzah ibn ‘Abdullah ibn ‘Umar ibn Al-Khattab, and other narrators who were classified by scholars as weak. However, Al-Bukhari and Muslim chose from the narrations of these weak reporters the acceptable ones that were devoid of subtle defects because a narrator may report many Hadiths, and commit mistakes in some of them. It is also possible that he may grow feeble-minded (in old age) and be labeled as Mukhtalit (confused in his narration due to poor memory). Al-Bukhari and Muslim took these factors into account and did not narrate except the Hadiths that were classified as authentic and devoid of defects.” [End of quote]

Likewise, the same goes for what you mentioned on the authority of Shaykh Ibn ‘Uthaymeen who said: “Among the books, on whose authenticity scholars have agreed, were Saheeh Al-Bukhari and Saheeh Muslim. All the Hadiths narrated therein are authentic so much that scholars said that the Hadiths recorded therein yield certain knowledge, not just conjecture because the Muslim nation received these Hadiths collections with full acceptance, and it is inconceivable for the Muslim nation to agree on a falsehood.” [End of quote]

Allah knows best.