Yosef Karo, Shulchan Aruch — Yoreh Deah 93
“ One should not cook dairy in a vessel in which one has cooked meat. If one cooks in it within 24 hours [of cooking the other kind of food] , it is forbidden where there is enough to give taste. However, if one waits for 24 hours before one cooks in it – it is a case of giving it [the food] a disgusting taste, and the cooked dish is permitted. As for the vessel, it is forbidden to cook in it both meat and also dairy. {Rama: but for any other food [a parve food] , it is permitted. The rule for the lid of the vessel is like the rule for the vessel itself. ”
