Narrated by Abu Dawud, 2457; At-Tirmidhi, 735 A brother said making up nafl fast is wajib.i gave him multiple hadith refuting bt he gave this hadith, when I said its daef,he said daeef can't be rejected because this incident was asked to aisha(r) later on and she said this is true. Please explain

Imam Ibn Bāz رحمه الله تعالى said: There is no obligation to make up the fast, but it is recommended. If someone intended to fast on Monday or Thursday and then broke the fast without a valid excuse, there is no sin upon him. However, if he makes it up later, that would be better. For example, if a guest came to him on Monday, or the heat was too severe, and he broke his fast—there is no problem. Al-ḥamdu lillāh, “the one who volunteers is in charge of himself” (meaning voluntary acts are not binding). It is not an obligation, but if he is able to make it up later, that is better. Yes.