Son by Four is a Latin music group from Puerto Rico, well known for their English U.S. pop hit "The Purest of Pain ". The group is now independent, and they founded their label SB4 Music Group in 2003.

"A Puro Dolor" is a song recorded by Puerto Rican band Son by Four. It was written by Omar Alfanno and released as the first single of the second studio album of the band in 2000. Two versions of the track were produced by Oscar Llord for the album; one as a salsa and the other as a ballad. The ballad version was arranged by Alejandro Jaén.