This historical painting is called The dream of the nun, painted by Karl Brulloff in 1831.
This highly idealized picture shows a young nun fast asleep and the mother superior checking in on her. She really ought to, because the girl is dream of a romantic love between her and some fair young man. Hardly suitable for a girl with a religious calling.
To distinguish what time it is that the picture is trying to convey is actually quite hard. The girl in the dream is wearing clothes and a hair-do that could suit the time the picture was done - but the man is less so. This is not the place do discuss male clothing, but let us just note that no man (perhaps except on the stage) would wear something like that man has put on.
But historical paintings were rally popular in the 19th century, and many times the artists knew very little about how things looked like in the era they portrayed and had to guess, imagine and use what they saw in their own time to make something that could pass for correct. After all, the buyers and viewers seldom knew more about it.
The painting is currently owned by the Russian museum in St. Petersburg, Russia.