Biography: Imam Bukhari
Imam Bukhari was a Mujtahid
Anwar Shah Kashmiri (Hanafi):

Maulana Anwar Shah Kashmiri Hanafi on Imam Bukhari’s Ijtihad

Maulana Anwar Shah Kashmiri Hanafi, about whom Anzar Shah Hanafi quotes Shaykh Ali in Naqsh Dawam Hayat Kashmiri (p. 290) as saying: «لو حلفت أنه أعلم بأبي حنيفة لما حنثت» "If I swore that he (Kashmiri) knew Abu Hanifa better than anyone, I would not be breaking my oath."

He (Anwar Shah Kashmiri) writes: «واعلم أن البخاري مجتهد لا ريب فيه» [Muqaddimah Fayd al-Bari 1/58] — "Know that Imam Bukhari was a Mujtahid; there is no doubt about it."

And in another place, refuting those who claim Imam Bukhari followed the Shafi’i school, he writes: «لكن الحق أن البخاري مجتهد» [Al-‘Urf al-Shadhi 1/126] — "But the truth is that Imam Bukhari was a Mujtahid."