Combining the fast
    of Dawood and fasting on Mondays and Thursdays
Question

                I know that fasting every other day is the
    best way of fasting as in the hadith that this is the fasting of Prophet Dawood, alyhi
    assalam..but, how can i fast Mondays and Thursdays, and also fast every other day
    like the Sunnah..? because sometimes Monday or Thursday doesn't fall in the order..like if
    i fast like the way Prophet Dawood did, i would fast for example: Monday, Wednesday,
    Friday, Sunday..etc. so sometimes Thursday doesn't fall in the order, or Monday..I hope my question is clear..
Praise be to Allah.Islam has brought different kinds of acts of worship,
    and this is part of the perfection of this religion. There are acts of worship which can
    be combined with others and other acts of worship which cannot be combined. Fasting on
    alternate days is one independent type of worship; it is a kind of voluntary fast, and it
    is the best kind.
Fasting on Mondays and Thursdays is another independent type of
    worship. It cannot be imagined that it is possible to combine the two on an ongoing basis.
    The better kind should be given preference, but a person should take his own situation and
    strength into account, so he should not start something that he will not be able to
    continue  in the case of naafil deeds  because the most beloved of deeds to
    Allaah is that which is continuous, even if it is little. And Allaah is the source of
    strength.