33 He very carefully showed reverence and obedience to St. Gregory II and his successors, and on occasion gave clear proof of this. Thus, for example, did he write to Pope St. Zachary, immediately on learning of the latter's succession to the papal throne: "Never have we heard of gladder tidings which brought us more joy than the news that the Supreme Judge had entrusted to Your Holiness the government of the Apostolic See and the care of the sacred canons. Lifting our arms in prayer, we thanked God. So, just as if we were kneeling before you, we earnestly pray that we may merit, in perfect harmony with the sacred canons, to be obedient servants of Your Holiness, as we were devoted and submissive disciples of Your predecessors in Peter's chair. I cease not to call and urge to obedience to the Apostolic See all who wish to keep the Catholic faith and union with the Church of Rome, and whomever God gives me as followers or disciples in my apostolate. "
Source: Ecclesiae Fastos (Vatican.va)