Answer:
(Fatwa: 1098/1098=M/1430)
If you have only intended to keep fast on every Monday and Thursday without making a vow (nazr), you are not required to keep fast in those days and you will not deserve sin or kaffarah if you leave it.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
