Hazrat Ali, Hazrat Ibn Mas'ud, and Hazrat Ibn Abbas (may Allah be pleased with them) state that the way to end the oath of Ila is through intercourse. Hazrat Ibn Mas'ud (may Allah be pleased with him) says that if there is an excuse due to old age, illness, or if he does not have access to his wife because of imprisonment, then verbal or heartfelt retraction is also sufficient.