Let us pray, brothers, to the Lord our God for our brother _____, who now suffers under severe hardships, that the goodness of the Lord may heal him with heavenly medicine. May he who has given the soul, also preserve it; through our Lord. 
To the almighty living God, who restores and strengthens all his works, let us pray, dear brothers, for our sick brother, that either in renewal or recovery the creature may feel the hand of the creator; in the man of his making may the tender Father recreate his work; through our Lord. 
O Lord, holy Father, author of the universe, almighty and eternal God, to whom all are alive. You bring the dead to life and call things that are not as those that are. Since you are the maker, in love do your work for this person you have fashioned; through our Lord. 
To God, in whose hands are the support of the living and the life of the dead, we pray that this infirm body may be cured and this soul be healed, that what he does not deserve by merit, he may receive by our prayers for your mercy’s sake; through our Lord. 
O God, you do not desire the death of a sinner but that he turn and live. Forgive the sins of this man who has turned to you with all his heart, and give him the grace of eternal life; through our Lord. 
O God, you always govern your creatures with tender affection. Hear our prayers for your servant _____, who is suffering from bodily sickness. Visit him with your deliverance, and give him the medicine of your heavenly grace; through our Lord. 
Source: The Book of Dimma, 7th century. Prayer #6 is also found in Gelasian sources.
Source of this version: Prayers from the Ancient Celtic Church, © 2018, Paul C. Stratman
Originals in Latin:
Oremus, fratres, dominum deum nostrum pro fratre nostro .n. quem duri adpresens malum langoris adulcerat, ut eum domini pietas caelestibus dignetur curare medicinis ; qui dedit animam det etsalutem, perdominum nostrum. 
Deum uiuum omnipotentem, cui omnia opera restaurare [et] confirmare facillimum est, fratres carissimi, profratre nostro infirmo supliciter oremus, quo creatura manum sentiat creatoris aut inreparando aut inrecipiendo ; inhomine suo pius pater opus suum recreare dignetur, perdominum nostrum. 
Domine, sancte pater, uniuersitatis auctor, omnipotens aeternae deus, cui cuncta uiuunt, qui uiuificas mortuos et uocas ea quae non sunt, tanquam ea quae sunt, tuum solitum opus, qui es artifex, pie exerce in hoc plasmate tuo, perdominum. 
Deum in cuius manu tam alitus uiuentis quam uita morientis, fratres dilectissimi, deprecemur, ut corporis huius infirmitatem sanet et animae salutem prestet; ut quod per meritum non meretur, misericordiae gratia consequatur, orantibus nobis, perdominum. 
Deus, qui non uis mortem peccatoris, sed ut conuertatur et uiuat, huic adte excorde conuerso peccata dimite, et perennis uitae tribu[e] gratiam, perdominum. 
Deus, qui facturam tuam pio semper do[mi]nares afectu, inclina aurem tuam suplicantibus nobis tibi; ad famulum tuum .n. aduersitate ualitudinis corporis laborantem placitus respice; uisita eum insalutare tuo, et caelestis gratiae ad medicamentum, per dominum.