All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Mu‘allaq Hadeeths in Saheeh Al-Bukhari fall into two categories:
1. Those that he narrated with a definitive form, for example: when he says so-and-so said such-and-such or mentioned such-and-such... This method of narrating Mu‘allaq Hadeeths is considered a judgment by Al-Bukhari that these Hadeeths are authentically attributed to the person they are attributed to. This is because he would never have definitively attributed something to a certain narrator unless he had verified the authenticity of that attribution to that narrator.
2. Those with a less definitive form, for example when he says, it was said or it was narrated on the authority of so and so... Hadeeths in this form are not necessarily authentic because this form of narration may be also used with Dha‘eef (weak) Hadeeths.
However, many of the Mu‘allaq Hadeeths narrated in Saheeh Al-Bukhari were also narrated by him with their Isnaads (chains of narrators) mentioned in full in other places in the same book as the Mawsool Hadeeths (those Hadeeths whose chains are fully connected). This was done for the sake of brevity and to avoid repetition.
Only 160 Mu‘allaq Hadeeths were not narrated by him as Miawsool Hadeeths, but Al-Haafith ibn Hajar proved that all of these are Mawsool Hadeeths in his book Taghleeq Al-Ta‘leeq. Also, he mentioned this fact briefly in the introduction to his other book Fat’h Al-Baari ‘Ala Saheeh Al-Bukhari.
It should be noted that the Hadeeths that Al-Bukhari attributed to some of his Shaykhs with a definitive form (such as the Hadeeth on musical instruments) were judged to be Muttasil (connected) Hadeeths in the part of the Isnaad that falls between Al-Bukhari and the Shaykh to whom he attributed the Hadeeth.
Allaah Knows best.