I just added this image to the Trombone History Timeline (16th century). The full image (full manuscript page) is also shown here for reference.

1599—Antwerp: An engraving from Graduale Romanum, published by Plantin and Moretus, depicts a group of singers accompanied by 4 instrumentalists, including one playing what may be a trombone (see below image; public domain). Special thanks to Aline Hopchet.