The Sabbath Early Kept in Scotland and Ireland

It seems to have been customary in the Celtic churches of early times, in Ireland as well as Scotland, to keep Saturday, the Jewish Sabbath, as a day of rest from labor [...]. In that case they obeyed the fourth commandment literally upon the seventh day of the week [...].

Moffat, James Clement, The Church in Scotland: a history of its antecedents, its conflicts and its advocates, from the earliest recorded times to the first assembly of the Reformed Church, Philadelphia: Presbyterian Board of Publication, 1882, p. 140.