The World Federation One Stop Fiqh

Ruling 750

If there is ample time for an adāʾ prayer, one can, during the prayer – in the event that he remembers he has an outstanding qaḍāʾ prayer to perform – change his intention to the qaḍāʾ prayer. However, [for this to be valid,] it must be possible to change the intention to a qaḍāʾ prayer; for example, if he has started to perform the ẓuhr prayer, he can change his intention to a qaḍāʾ ṣubḥ prayer only if he has not yet reached the rukūʿ of the third rakʿah.