When imam Bukhari mentions a muʿallaq hadith with sigha al-jazm, then it is his ruling that it is authentic from the one to whom it is attributed - Ibn al-Salah

Ulum al-Hadith cover - Ibn al-Salah
Muʿallaq hadith with sigha al-jazm - Ibn al-Salah (Ulum al-Hadith) part 1
Muʿallaq hadith with sigha al-jazm - Ibn al-Salah (Ulum al-Hadith) part 2