Is it cited in Ṣaḥīḥ Al-Bukhārī that the Dawn Prayer (Ṣalāt al-Ṣubḥ) consists of four rak‘as, as indicated by the hadith narrated by ‘Abdullāh ibn Mālik ibn Buḥaynah, reported in al-Bukhārī’s book?

     The hadith reported in Ṣaḥīḥ Al-Bukhārī  on the authority of ‘Abdullāh ibn Buḥaynah does not indicate that the Dawn Prayer (Ṣalāt al-Ṣubḥ) consists of four rak‘as, but rather indicates that the Prophet (PBUH) disapproved of the act of someone whom he found praying two rak‘as immediately after the second call for the Dawn Prayer (Ṣalāt al-Ṣubḥ) had been made.

     According to the complete text of the hadith as in Ṣaḥīḥ Al-Bukhārī, “the Messenger of Allah (PBUH) saw a man praying two rak‘as after the second call for prayer had been made. When Allah's Messenger (PBUH) completed his prayer, the people gathered around the man, and Allah's Messenger (PBUH) said to him, “Did you perform four rak‘as for the Dawn Prayer (Ṣalāt al-Ṣubḥ)?  Did you perform four rak‘as for the Dawn Prayer (Ṣalāt al-Ṣubḥ)?”

     The meaning of the hadith is that the Prophet (PBUH) disapproved of the man’s act of performing supererogatory prayer while the obligatory prayer was about to be performed. There is nothing in the narration that implies the claim made in the question or even raises doubts about it. So, the one who asked the question needs to reconsider his position and is advised to read any text carefully before raising questions or provoking doubts about it.