Is there any reference in the Holy Bible to confession as being necessary before partaking of Holy Communion? Also, is there a reference to confessing our sins to a priest?
Confession is considered a holy Sacrament in the Coptic Orthodox Church. To the Orthodox faithful, Confession means verbal confession by the person who is humbly confessing before a Confessor and repenting of the sins and mistakes he has made. This sets forth the absolution and forgiveness of sins.
When the Lord Jesus Christ instituted the Sacrament of Repentance and Confession, He said, "Assuredly, I say to you, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven." (Matthew 18:18). Please also read (Matthew 16:19).
Following the Holy Resurrection, the Lord Jesus Christ said, "So Jesus said to them again, 'Peace to you! As the Father has sent Me, I also send you.' And when He had said this, He breathed on them, and said to them, 'Receive the Holy Spirit. If you forgive the sins of any, they are forgiven them; if you retain the sins of any, they are retained'" (John 20:21-23).
By saying this, the Lord Jesus Christ gave them the authority by the Holy Spirit of binding sins or loosing them, according to the circumstances and the degree of repentance of the confessing person.
Confession was practiced in the Old Testament (Lev 5:5,6), (Mt 3:6) and the apostles themselves practiced this authority (Acts 19:18), (1 Cor 5:5), (2 Cor 2:6,7), (1 Tim 5:20), and (James 5:16).
Also an important point to note, is that the priest actually doesn't of himself absolve the person confessing; but he says, "May God absolve you"; as he does not absolve out of his own power, but obtains the absolution from God, the origin of all absolution and forgiveness.
We should practice confession before communion as our teacher St. Paul taught us in 1 Cor 11:27-29.
There is a very good book to read, "Repentance and Confession” the third Sacrament written by His Grace Bishop Mettaous. Also you can find different aspects of the Sacrament of Confession in other questions in this category.