.GOD, who makest worthy of the unworthy, just and holy of sinners, and clean of the unclean, cleanse my heart and body from all taint and defilement of sin, and make me a worthy and strenuous minister at thy holy altars; and mercifully grant that on this altar, to which I unworthy make approach, I may offer a sacrifice acceptable and pleasing to thy loving-kindness, for my sins and offences, and for my innumerable daily transgressions, and likewise for the washing away of the sins of all Christian people. And may my desire be acceptable to thee, through him who offered himself a sacrifice for us to thee his God and Father, Who liveth and reigneth with thee and the Holy Ghost, one God, world without end. Amen.
This prayer of the priest before Mass appears in a 1526 edition of the Sarum Missal. In the Missal this prayer is located between Holy Saturday and Easter Day. It would be an appropriate prayer before Mass for all priests.