Part of the Canon of the Mass, just after the Hanc Igitur and before the Consecration, said by the celebrant.
A the word "vouchsafe", the crucifer rings the bell and all servers bow low. The acolyte and deacon kneel at the altar.
VOUCHSAFE, O God we beseech thee, in all things to make this oblation blessed, approved, and accepted, a perfect and worthy offering; that it may become for us the Body and Blood of thy dearly beloved Son, our Lord Jesus Christ.