Even J.S. Bach did reuse some of his works. For example parts of the famous Christmas oratorio are originally from a secular cantanta: https://en.m.wikipedia.

Even J.S. Bach did reuse some of his works. For example parts of the famous Christmas oratorio are originally from a secular cantanta: https://en.m.wikipedia.org/wiki/Tönet,_ihr_Pauken!_Erschallet,_Trompeten!_BWV_214 https://en.m.wikipedia.org/wiki/Tönet,_ihr_Pauken!_Erschalle...