Lascia ch'io pianga is a famous aria by George Frideric Handel included in the opera "Rinaldo".
The melody wasn't originally written for this opera though: Handel used it first as an instrumental piece in 1705 for the opera Almira, and later re-used it for an oratorio aria, "Il trionfo del tempo e del disinganno", 2 years later ("Lascia la spina, cogli la rosa" was the first verse).
After 4 years, in 1711, Handel changed the lyrics and recycled this theme once again for the "Rinaldo": this opera was a major success in Handel's career, and therefore we are used to refer to this aria with the title "Lascia ch'io pianga".

We have prepared for you the karaoke and study versions (with unmuted vocal line) in F major, the original key: