20 It is necessary to pass over in silence many of the other writings of St. Francis in which however we may no less discover "that heaven-sent doctrine which, like a stream of living water, has watered the vineyard of the Lord . . . and has helped greatly in achieving the well-being of the people of God." ( Apostolic Letter of Pius IX, 16 Nov. 1877) But, We cannot afford not to speak of his work entitled Controversies , in which unquestionably there is to be found a "full and complete demonstration of the truth of the Catholic Religion." ( Apostolic Letter of Pius IX, 16 Nov. 1877)
Source: Rerum Omnium Perturbationem (Vatican.va)