Instrumental version of Bellini's famous aria from the opera "Norma": Casta diva.
The performance from Maria Callas is much probably the most famous - and notable - among the thousands of recorded performances available.
The libretto is from Felice Romani, and here are the original italian lyrics for the aria:

Casta Diva che inargenti
Queste sacre antiche piante,
A noi volgi il bel sembiante
Senza nube e senza vel.

Tempra o Diva,
Tempra tu de' cori ardenti,
Tempra ancor lo zelo audace,
Spargi in terra quella pace
Che regnar... » ... sing it!