"Muttafaq ʿalayh" (agreed upon) means a hadith that both al-Bukhari and Muslim narrated in their two Sahih collections through a Companion. Because the Ummah received both books with acceptance, scholars place a muttafaq ʿalayh report at the very highest rank of authenticity, above a hadith reported by only one of them. For example, the hadith "Islam is built upon five..." is agreed upon, being found in both Sahihs.
Evidence — the daleel
Sahih al-Bukhari 8 ṢaḥīḥSahih Muslim 16 Ṣaḥīḥ
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.