Can One Fast Only on Mondays?
Question

I am not able to fast on Thursdays for certain reasons. Is it sufficient for me to fast on Monday every week or is it essential to fast both of them?
Praise be to Allah.Shaykh Ibn Baz (may Allah have mercy on him) said:
“There is nothing wrong with fasting on one of the two days (Monday or Thursday) and not the other. Fasting on these two days is recommended and is not obligatory, so if someone fasts on both of them or one of them, he is doing a great good deed. It is not obligatory to fast on both of them ; rather that is recommended  because of the authentic Hadiths concerning that which were narrated from the Prophet (blessings and peace of Allah be upon him). And Allah is the source of strength.” (Majmu` Fatawa Ash-Shaykh Ibn Baz, 15/387)
And Allah knows best.