被き伏す蒲団や寒き夜やすごき
kazuki fusu futon ya samuki yo ya sugoki[1]
lying covered
under futon, yet
the night—so cold
—Bashō[2]
The breaks in my translation in the second and third lines are the same as Bashō uses. Normally cutting words come at the end of line 1 or line 2, but in this case we get two of them right in the middle of line 2 and line 3. It is a bit unusual, but Bashō purposely did it to give the feeling of stress.
It’s not Bashō who is so cold, nor is it the winter temperature that is causing the cold. He wrote this haiku for his student Rika, whose wife had died the previous year. He imagined how lonely and sad Rika must feel without his beloved wife on a cold winter night.
I’m sure you all know what a futon is. Unlike the Western couch-bed thing we call a futon, a Japanese futon is a nice and comfortable mattress laid directly on the ground for sleeping covered with a thick, warm blanket. The mattress is called a shikibuton and blanket a kakebuton, but confusingly either mattress or blanket by themselves can also be referred to as futon.
At the time Bashō wrote this, in Edo, futon covers were not a common thing. Typically poor people slept around the cooking area (irori), which was warm, and slept close together to warm themselves with each others’ body heat. On especially cold nights they might sleep under a quilt of seaweed or other cheap material.
So when Bashō says sleeping under futon, he isn’t referring to a kakebuton—it is literally sleeping under the futon. A cold night for Rika—colder still without his wife.
Rika, by the way, is the student who helped Bashō plant the banana trees (bashō) at his hermitage, from which he took his famous pen name.
