Bede's Ecclesiastical History of England, ed. by A.M. Sellar, , at sacred-texts.com
AMONG those who were present at this synod, and confirmed the decrees of the Catholic faith, was the venerable John, archchanter of the church of the holy Apostle Peter,and abbot of the monastery of the blessed Martin, who had come lately from Rome, by order of Pope Agatho, together with the most reverend Abbot Biscop, surnamed Benedict,of whom mention has been made above. For the said Benedict, having built a monastery in Britain, in honour of the most blessed chief of the Apostles, at the mouth of the river Wear, went to Rome with Ceolfrid,his companion and fellow-labourer in that work, who was after him abbot of the same monastery; he had been several times before at Rome, and was now honourably received by Pope Agatho of blessed memory; from whom he also asked and obtained, in order to secure the immunities of the monastery which he had founded, a letter of privilege confirmed by apostolic authority, according to what he knew to be the will and grant of King Egfrid, by whose consent and gift of land he had built that monastery.
He was also allowed to take the aforesaid Abbot John with him into Britain, that he might teach in his monastery the system of singing throughout the year, as it was practised at St. Peter’s at Rome. The Abbot John did as he had been commanded by the Pope, teaching the singers of the said monastery the order and manner of singing and reading aloud, and committing to writing all that was requisite throughout the whole course of the year for the celebration of festivals; and these writings are still preserved in that monastery, and have been copied by many others elsewhere. The said John not only taught the brothers of that monastery, but such as had skill in singing resorted from almost all the monasteries of the same province to hear him, and many invited him to teach in other places.
Besides his task of singing and reading,, he had also received a commission from the Apostolic Pope, carefully to inform himself concerning the faith of the English Church, and to give an account thereof on his return to Rome. For he also brought with him the decision of the synod of the blessed Pope Martin, held not long before at Rome,with the consent of one hundred and five bishops, chiefly to refute those who taught that there is but one operation and will in Christ, and he gave it to be transcribed in the aforesaid monastery of the most religious Abbot Benedict. The men who followed such opinion greatly perplexed the faith of the Church of Constantinople at that time; but by the help of God they were then discovered and overcome.Wherefore, Pope Agatho, being desirous to be informed concerning the state of the Church in Britain, as well as in other provinces, and to what extent it was clear from the contagion of heretics, gave this matter in charge to the most reverend Abbot John, then appointed to go to Britain. The synod we have spoken of having been called for this purpose in Britain, the Catholic faith was found untainted in all, and a report of the proceedings of the same was given him to carry to Rome.
But in his return to his own country, soon after crossing the sea, he fell sick and died; and his body, for the sake of St. Martin, in whose monastery he presided, was by his friends carried to Tours, and honourably buried; for he had been kindly entertained by the Church there on his way to Britain, and earnestly entreated by the brethren, that in his return to Rome he would take that road, and visit their Church, and moreover he was there supplied with men to conduct him on his way, and assist him in the work enjoined upon him. Though he died by the way, yet the testimony of the Catholic faith of the English nation was carried to Rome, and received with great joy by the Apostolic Pope, and all those, that heard or read it.