Fathwa - Fasting in Ramadhaan with the intention of fulfilling a vow

Question
Is it permissible to fast in Ramadan with the intention of fulfilling
a specific vow?
Answer
All perfect praise be to Allaah, The Lord of the worlds. I testify
that there is none worthy of worship except Allaah, and that Muhammad,
is His slave and messenger.
If the intended meaning of the question is that he fasts in Ramadhaan
with two intentions or with the intention of fulfilling a vow in case
it is permissible for him not to fast, then this is impermissible. The
time of Ramadhaan is specific for its sake. Nothing may be associated
with it and it may not be replaced with anything else.
An-Nawawisaid: Ash-Shaafi'i and his companionssaid: "The month of
Ramadhaan should be exclusively for fasting Ramadhaan only, so
nothing else should be associated with it. If a presiding resident,
traveler or one who is sick intends to fast for expiation, fulfill a
vow, make up (a missed fast), voluntary fasting or intends to fast
absolutely without specification, then his intention and fasting are
both invalid for what he intended and for Ramadhaan. This is what was
stated and confirmed by his companions.
Allaah Knows best.