"On the evening of that day, the first day of the week," Jesus showed himself to his apostles. "He breathed on them, and said to them: 'Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained"' (Jn 20:19, (22-23).
Source: Catechism of the Catholic Church (Vatican.va)