Why would they need biblical permission for enacting the sacraments (e.g. Baptism, Reconciliation, The Sacrifice of the Eucharist)? They were doing those things for years before the Gospels were written down.
But anyway - here you go:
"If you forgive anyone his sins, they are forgiven; if you withhold forgiveness from anyone, it is withheld."
Greek...
"If you forgive anyone his sins, they are already forgiven; if you withhold forgiveness from anyone, it is already withheld."
It was the proclamation that the meaning of Christ's death is that sins were forgiven to those who received His gift, or not forgiven to those who do not.
It was not a sacrament that bestowed forgiveness or withheld forgiveness.
John 3:16 is the pathway to Heaven. It is exclusive of all other "methods".