The Second Pentecost
On the feast of Our Lady's Assumption, 1217, St. Dominic, in his burning zeal for the spread of Truth, sent his sixteen followers on their missions in the same manner as the Apostles, without wallet and on foot. Saints Peter and Paul had previously appeared to St. Dominic in a vision with the command to go and preach, "for unto this has God chosen thee." Some have referred to this dispersion of the brethren as a second Pentecost.
From Pope Honorius III to Saint Dominic on December 22, 1216:
We considering that the brethren of your Order will be the champions of the faith and true lights of the world, do confirm the Order in all its lands and possessions, present and to come, and we take the Order itself, with all its goods and rights under our protection and government.
h/t Devotions to Saint Dominic, compiled by Rev. Bertrand Wilberforce, O.P.