Sacerdotii nostri primordia ("From the beginning of our priesthood") was the second encyclical of Pope John XXIII, issued 1 August 1959. It commemorated the 100th anniversary of the death of St. John Vianney, the patron saint of priests.
See also List of encyclicals of Pope John XXIII Saint John Vianney's prayer to Jesus
References
text on Vatican website.