Muhaqqaq Masala

When does Kaffarah (expiation) become obligatory?

If a legally responsible (Mukallaf) person, while remembering the fast, intentionally and without any doubt, eats or drinks any desired food or beneficial medicine, or engages in sexual intercourse, and thereby invalidates the fast in Ramadan, then both Qaza (making up the fast) and Kaffarah (expiation) become obligatory upon them. (Book: Kitab an-Nawazil / Vol: 6 / Pg: 401)