Cantiga 2 of the Cantigas de Santa Maria of Alfonso X

Hildefonsus of Toledo
   The Virgin gave a vestment to a Spanish priest named Ildefonso.
   Ildefonso preached well and wrote that Mary was a Virgin, although Jews and heretics challenged this notion.
   One day, while he was walking in a procession with King Reccesvinth, St Leocadia appeared before them. She told Ildefonso: "my Lady lives through you."
   The Virgin gave him an alb to wear on her feast days.
   She warned him that no one else was to sit in his chair or to wear the garment.
   His successor, Archbishop Siagrio, put on the alb and was killed immediately.


Source

List of Cantigas de Santa Maria