The Golden Legend of Cosmas and Damian
(...)
"Felix, the eighth pope after Saint Gregory, did do make a noble church at Rome of the saints Cosmo and Damian,
and there was a man which served devoutly the holy martyrs in that church, who a canker had consumed all thigh.
And as he slept, the holy martyrs Cosmo and Damian appeared to him their devout servant, bringing with them an instrument and ointment of whom that one said to that other : where shall we have flesh when we have cut away the rotten flesh to fill the void place ?
Then that other said to him : there is an Ethiopian that this day is buried in the churchyard of St Peter ad Vincula, which is yet fresh, let us bear this thither, and take we out of that morian's flesh and fill this place withal.
Ans so they fetched the thigh of the sick man and so changed that one for the other.
And when the sick man awoke and felt no pain, he put forth his hand and felt his leg without hurt, and then took a candle, and saw well that it was not his thigh, but that it was another.
And when he was well come to himself, he sprang out of his bed for joy, and recounted to all the people how it was happed to him, and that which he had seen in his sleep, and how he was healed.
And they sent hastily to the tomb of the dead man, and found the thigh of him cut off, and that other thigh in the tomb instead of his.
Then let us pray unto these holy martyrs to be our succour and help in all our hurts, blechures and sores, and that by their merits after this life we may come to everlasting bliss in heaven.
Amen."
The Golden Legend of Cosmas and Damian by Jacobus de Voragine