Question: I have heard that it is written in one of the commentary on
Birghiwi's Wasiyyatnama, "A person who has
fard salats to make up should perform
sunnat salats with the intention of both performing
sunnat salats and making up his/her
qada salats." Is it true?
ANSWERYes, it is true. In the original text that we have provided as a link below, it is stated that it is necessary for one who has many
qada salats to perform
sunnat salats with the intention of both performing
sunnat salats and making up one's
qada salats. If one performs the
sunnat salat of
Salat al-Maghrib as three
rak'ats [with the intention of making up a missed
Salat al-Maghrib] and performs the post-
fard sunnat salat of
Salat al-Isha as three
rak'ats [with the intention of making up a missed
Salat al-Witr] and recites
Qunut prayers [in the third
rak'at], it is written therein that one will have performed both
sunnat salats and
qada salats. The reason for this is that what matters is not the number of
rak'ats but performing an extra
salat in addition to a
fard salat. Performing three
rak'ats, too, fulfills the
sunnat. In order to emphasize the validity of double intention, it is also stated therein,
"Two duties can be lifted by a single act, just as sajda at-tilawat can be done with a ruku' in salat." (p. 263)Click here for the original text 
