Aeterna Dei Sapientia §44

⁴⁴ There is, moreover, another essential safeguard of the Church's visible unity which did not escape that notice of this saintly Pope: that supreme authority to teach infallibly, which Christ gave personally to Peter, the prince of the apostles, and to his successors. Leo's words are quite unequivocal: "The Lord takes special care of Peter; He prays especially for Peter's faith, for the state of the rest will be more secure if the mind of their chief be not overthrown. Hence the strength of all the rest is made stronger in Peter, and the assistance of divine grace is so ordained that the stability which through Christ is given to Peter, should through Peter be transmitted to the other apostles." (39)