Scotland
They held that Saturday was properly the Sabbath on which they abstained from work. "Celtic Scotland," Vol. 2, p. 350
"They worked on Sunday, but kept Saturday in a sabbatical manner...These things Margaret abolished." A History of Scotland from the Roman Occupation," Vol.1, p. 96.
"It was another custom of theirs to neglect the reverence due to the Lord's day, by devoting themselves to every kind of worldly business upon it, just as they did upon other days. That this was contrary to the law, she (Queen Margaret) proved to them as well by reason as by authority. 'Let us venerate the Lord's day,' said she, 'because of the resurrection of our Lord, which happened upon that day, and let us no longer do servile works upon it; bearing in mind that upon this day we were redeemed from the slavery of the devil. The blessed Pope Gregory affirms the same.'" Life of Saint Margaret, Turgot, p. 49 (British Museum Library)
(Historian Skene commenting upon the work of Queen Margaret) "Her next point was that they did not duly reverence the Lord's day, but in this latter instance they seemed to have followed a custom of which we find traces in the early Church of Ireland, by which they held Saturday to be the Sabbath on which they rested from all their labours." Skene, "Celtic Scotland," Vol.2, p. 349
Scotland And Ireland
"T. Ratcliffe Barnett, in his book on the fervent Catholic queen of Scotland who in 1060 was first to attempt the ruin of Columba's brethren, writes: 'In this matter the Scots had perhaps kept up the traditional usage of the ancient Irish Church which observed Saturday instead of Sunday as the day of rest.'" Barnett, "Margaret of Scotland: Queen and Saint," p.97
Council Of Clermont
"During the first crusade, Pope Urban II decreed at the council of Clermont (A.D.1095) that the Sabbath be set aside in honour of the Virgin Mary." History of the Sabbath, p.672
Constantinople
"Because you observe the Sabbath with the Jews and the Lord's Day with us, you seem to imitate with such observance the sect of Nazarenes." Migne, "Patrologia Latina," Vol. 145, p.506; also Hergenroether, "Photius," Vol. 3, p.746. (The Nazarenes were a Christian denomination.)
Greek Church
"The observance of Saturday is, as everyone knows, the subject of a bitter dispute between the Greeks and the Latins." Neale, "A History of the Holy Eastern Church," Vol 1, p. 731. (Referring to the separation of the Greek Church from the Latin in 1054)