Please answer the following question: Given the following context:  For a French composer of the 19th century, opera was seen as the most important type of music. Saint-Saëns's younger contemporary and rival, Massenet, was beginning to gain a reputation as an operatic composer, but Saint-Saëns, with only the short and unsuccessful La princesse jaune staged, had made no mark in that sphere. In February 1877, he finally had a full-length opera staged. His four-act "drame lyricque", Le timbre d'argent ("The Silver Bell"), to Jules Barbier's and Michel Carré's libretto, reminiscent of the Faust legend, had been in rehearsal in 1870, but the outbreak of war halted the production. The work was eventually presented by the Théâtre Lyrique company of Paris; it ran for eighteen performances.The dedicatee of the opera, Albert Libon, died three months after the premiere, leaving Saint-Saëns a large legacy "To free him from the slavery of the organ of the Madeleine and to enable him to devote himself entirely to composition". Saint-Saëns, unaware of the imminent bequest, had resigned his position shortly before his friend died. He was not a conventional Christian, and found religious dogma increasingly irksome; he had become tired of the clerical authorities' interference and musical insensitivity; and he wanted to be free to accept more engagements as a piano soloist in other cities. After this he never played the organ professionally in a church service, and rarely played the instrument at all. He composed a Messe de Requiem in memory of his friend, which was performed at Saint-Sulpice to mark the first anniversary of Libon's death; Charles-Marie Widor played the organ and Saint-Saëns conducted. In December 1877, Saint-Saëns had a more solid operatic success, with Samson et Dalila, his one opera to gain and keep a place in the international repertoire. Because of its biblical subject, the composer had met many obstacles to its presentation in France, and through Liszt's influence the premiere was given at Weimar in a German translation. Although the work eventually became an...  answer the following question:  What piece was composed as a tribute to Albert Libon?
A:
Messe de Requiem