Nafl fasts should be kept according to one’s ability. For example: one should fast on the 13th, 14th and 15th (known as Ayyaam-e-Beedh) of every Islamic month; the six fasts during the month of Shawwaal; the nine fasts of Zil-Hajj or only on the Day of Arafah (9th Zil-Hajj); the two days of Muharram (9th and 10th or 10th and 11th), and the 15th of Sha’baan.