35 Rightly therefore, on the occasion of the twelfth centenary of the beginning of this glorious martyr's apostolic mission among the peoples of Germany, Our predecessor of immortal memory, Benedict XV, wrote to the bishops of that nation: "Moved by this strong faith, inflamed by this piety and charity, Boniface most resolutely preserved that singular fidelity and devotion towards the Apostolic See which he seems to have first drawn from the contemplative exercises of the monastic life in his fatherland, which on the point of advancing into the open struggle of the apostolic life, he pledged by a sacred vow at Rome, over the tomb of Blessed Peter, the Prince of the Apostles, and which finally he carried with him into the thick of the hazardous battle as the form of this apostolate and the rule of the mission he had undertaken. This same fidelity to the Apostolic See he never ceased to recommend strongly to all those whom he had brought forth through the Gospel, and to inculcate with such zeal that he seemed to have left it as his last will and testament."
Source: Ecclesiae Fastos (Vatican.va)