Aldfrith appears to have had the support of leading ecclesiastics, most notably his half-sister Ælfflæd and the highly respected Bishop Cuthbert. He is known to have received confirmation at the hands of Aldhelm, later the Bishop of Sherborne in the south-western Anglo-Saxon Kingdom of Wessex. Aldhelm too had received an Irish education, but in Britain, at Malmesbury. Correspondence between the two survives, and Aldhelm sent Aldfrith his treatise on the numerology of the number seven, the "Epistola ad Acircium". Aldfrith also owned a manuscript on cosmography, which (according to Bede) he purchased from Abbot Ceolfrith of Monkwearmouth-Jarrow in exchange for an estate valued at eight hides. Aldfrith was a close friend of Adomnán, Abbot of Iona from 679, and may have studied with him. In the 680s Aldfrith twice met with Adomnán, who came to seek the release of the Irish captives taken in Berht's expedition of 684. These were released and Adomnán presented Aldfrith with a copy of his treatise "De Locis Sanctis" ("On the Holy Places"), a description of the places of pilgrimage in the Holy Land, and at Alexandria and Constantinople. Bede reports that Aldfrith circulated Adomnán's work for others to read.