The Nuttall Encyclopedia
The doctrine of one Sabellius, who, in the third century, denied that there were three persons in the Godhead, and maintained that there was only one person in three functions, aspects, or manifestations, at least this was the form his doctrine assumed in course of time, which is now called by his name, and is accepted by many in the present day.
Wood, James, ed. Entry for 'Sabellianism'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/s/sabellianism.html. Frederick Warne & Co Ltd. London. 1900.