The World Federation One Stop Fiqh

Ruling 1594

If on a night of the month of Ramadan someone knows that he will not have time to perform ghusl or tayammum, yet intentionally becomes junub, his fast is invalid and qaḍāʾ and kaffārah become obligatory for him [i.e. he must keep a fast after the month of Ramadan and give recompense as well].