The “agreed-upon” ḥadith
A ḥadith gains added prestige when it is recorded in either of the two Ṣaḥīḥ collections; if it is found in both, its rank is higher, its standing greater, and its significance weightier still. This category constitutes the first of the seven levels of sound ḥadith already mentioned. Scholars of the Sunnah, whether specialists in ḥadith or others, commonly refer to it with the expressions “muttafaq ʿalayh” (agreed upon) or “akhrajāh” (recorded by both).
I know of no one who uses the term “muttafaq ʿalayh” for anything other than agreement between al-Bukhārī and Muslim alone—apart from al-Majd Ibn Taymiyyah, the grandfather of Shaykh al-Islām Ibn Taymiyyah. In his Muntaqā al-Akhbār, which al-Shawkānī annotated in Nayl al-Awṭār, he intends by “muttafaq ʿalayh” the agreement of al-Bukhārī, Muslim, and Aḥmad. For a report related only by the two Shaykhs (al-Bukhārī and Muslim) he uses the phrase “akhrajāh.”
That the agreed-upon ḥadith occupy the summit of authenticity is well-known among ḥadith scholars. After listing the seven categories of sound reports, Abū ʿAmr Ibn al-Ṣalāḥ said in his ʿUlūm al-Ḥadīth:
“These are the principal divisions, and the highest of them is the first, about which the ḥadith specialists frequently say, ‘ṣaḥīḥ, muttafaq ʿalayh.’ By this they mean agreement between al-Bukhārī and Muslim, not a consensus of the whole community—yet the latter necessarily follows, for the ummah has unanimously received whatever the two of them agreed upon with acceptance. This category is indisputably authentic, and both certain and inferential knowledge are attained through it.” End quote.
The agreed-upon ḥadith have been the subject of independent compilations, the most comprehensive and carefully edited of which is al-Luʾluʾ wa-l-Marjān fīmā ittafaqa ʿalayhi al-Shaykhān by Shaykh Muḥammad Fuʾād ʿAbd al-Bāqī. He completed its compilation in 1367 AH; it is published in three volumes and contains 1,906 agreed-upon reports. He arranged it according to the order of Ṣaḥīḥ Muslim, recording each ḥadith in Muslim’s wording and then indicating the closest wording in al-Bukhārī where the two concur. When a report is repeated, he notes the book and number in al-Bukhārī, together with the chapter and its number in that book.