This is indeed Death and Albert, from Mort
Death strode into the stable, stooping a little to clear the ceiling. Albert nodded, not in any
subservient way, Mort noticed, but simply out of form. Mort had met one or two servants, on the rare
occasions he’d been taken into town, and Albert wasn’t like any of them. He seemed to act as though
the house really belonged to him and its owner was just a passing guest, something to be tolerated like
peeling paintwork or spiders in the lavatory. Death put up with it too, as though he and Albert had
said everything that needed to be said a long time ago and were simply content, now, to get on with
their jobs with the minimum of inconvenience all round. To Mort it was rather like going for a walk
after a really bad thunderstorm—everything was quite fresh, nothing was particularly unpleasant, but
there was the sense of vast energies just expended.
I found it by searching for discworld old couple "said everything"