It is a detail from a fresco, The Matyrdom of St Christopher by Andrea Mantegna.

https://www.freeart.com/gallery/m/mantegna/mantegna11.html

It's from a church in Padua, Italy, painted 1453-57 with several scenes from the life of the saint. St Christopher got himself into trouble preaching in pagan Lycia (modern Turkey) and was sentenced to death by the king. The particular scene depicts St Christopher being subjected to various acts of violence before being executed, including being beaten by iron rods, branded, and sat on an iron stool above a fire, all of which he miraculously endures unharmed. The king then orders forty archers to let loose at him, but the arrows just hang in mid-air until one of them changes direction and shoots the king through the eye, which is what we're seeing in the detail.

All this info is found in the Golden Legend, a medieval collection of saintly biographies. You can read the text here:

https://sourcebooks.fordham.edu/basis/goldenlegend/GoldenLegend-Volume4.asp#Christopher