He makes his only historical appearance as Macbeth Rosmarkensis Episcopus (i.e. "Mac Bethad, Bishop of Rosemarkie") in a list of witnesses to a charter granted by King David I of Scotland to the Church of Dunfermline, confirming the previous rights of that church.
hiː mˌeɪks hɪz ˈoʊnli hɪstˈɔːɹɪkəl ɐpˈɪɹəns æz məkbˈɛθ ɹˌɑːzmɑːɹkˈɛnsɪs ᵻpˈɪskɑːpəs ˈaɪ.ˈiː. "mˈæk bˈɛθæd, bˈɪʃəp ʌv ɹˈoʊzmɑːɹki"ɪn ɐ lˈɪst ʌv wˈɪtnəsᵻz tʊ ɐ tʃˈɑːɹɾɚ ɡɹˈæntᵻd baɪ kˈɪŋ dˈeɪvɪd aɪ ʌv skˈɑːtlənd tə ðə tʃˈɜːtʃ ʌv dˈʌnfɚmlˌaɪn, kənfˈɜːmɪŋ ðə pɹˈiːviəs ɹˈaɪts ʌv ðæt tʃˈɜːtʃ.