How does one make up the days one does not know the number of?

Question: I broke my fast during one of the years on the days when my menstrual period came, and I have not been able to fast until now. Many years have passed, and I want to make up the debt of fasting that is upon me, but I do not know how many days are owed. What should I do?

Answer: You have three things to do:
The first thing: repent to Allah for this delay, feel remorse for the laxity that has passed, and resolve not to return to such a thing; for Allah says: [Surat al-Nur: 31]. This delay is a sin, and repentance to Allah for it is obligatory.
The second thing: hasten to fast according to your estimate, for Allah does not burden a soul beyond its capacity. What you think you left of days, you must make up. If you think it was ten days, fast ten days. If you think it was more or less, fast according to your estimate; for Allah the Exalted said: [Surat al-Baqarah: 286] and He said (peace and blessings be upon him) : [Surat al-Taghabun: 16].
The third thing: feed a poor person for each day, if you are able to do so. The entire amount may be given to one poor person. If you are poor and cannot afford to feed them, then nothing is required of you except fasting and repentance. The obligatory feeding for each day is half a sa' (a dry measure of about 3 kg) of the staple food of the land, which amounts to one and a half kilograms for one who is able to do so.