constitutes a large corpus of rigorously authenticated hadith from the Messenger of Allah ﷺ.

What the two scholars, al-Bukhari and Muslim—may Allah have mercy on them—both transmitted is ranked higher than what either one of them narrated on his own. Accordingly, the sound hadith in relation to what al-Bukhari and Muslim recorded or omitted may be arranged into seven levels:

1. That which both al-Bukhari and Muslim agreed upon;
2. That which is unique to al-Bukhari;
3. That which is unique to Muslim;
4. Reports that meet the joint criteria of al-Bukhari and Muslim but were not included by either of them;
5. Reports that meet the criteria of al-Bukhari alone but were not included by him;
6. Reports that meet the criteria of Muslim alone but were not included by him;
7. Reports that are absent from the two Sahihs and do not satisfy their specific criteria yet are still authentic.

These, then, are the seven tiers of ṣaḥīḥ hadith, the highest of which—as mentioned—is what al-Bukhari and Muslim both narrated, and the best