Saint Bede the Venerable (d. 733)
Although Mary the Mother of God had not yet given the 15 Mysteries of the Holy Rosary (Our Lady's Psalter) to Saint Dominic, prayer beads were being used by Christians as early as the eighth century.
Today, in the old calendar, is the feast of Saint Bede the Venerable (d. 733). Saint Bede attests that churches and public places in France and England had prayer beads available for the faithful to use.
Source: O'Reilly, Bernard. True Men as We Need Them: A Book of Instruction for Men in the World. New York: P.J. Kennedy and Sons. (1878) p. 217.