 He is also described as having a close and trusted Christian friend called "Abd al-Masih ibn Ishaq al-Kindi" (which translates as "Servant of the Messiah, son of Isaac, from the tribe Banu Kindah").Muir acknowledged difficulties in obtaining a reliable version of the Arabic text, but he defended the authenticity of the work, noting that the "Apology" was quoted by Abu-Rayhan Biruni around the year 1000 as the Epistle of "Abd al Masîh ibn Ishâc, Al Kindy".Both Muir and van Koningsveld favour a ninth-century date for the Apology.