Praying the post-Sunnah prayer between the two combined prayers
26-5-2011 | IslamWeb
Question:
Assalaam 'Alaykum! Here in UK, we normally combine the maghrib & isha in the masjid during Summer due to late disappearance of red twilight, i.e. the time of Isha is too close to Fajr. Well, I would like to know if we pray the Magrib & Isha one after the other with an Iqamah separating between them nothing else, the How would I be able to pray the 2 raka'ah sunnah, that's normally prayed after maghrib & Isha? Why can't I pray the 2 raka'ah sunnah after the maghrib salah & then pray Isha, can you provide me the proof, please.
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.
First of all, it should be mentioned that what some Muslims used to do in non-Muslim countries, i.e. combining between the Maghrib and ‘Ishaa’ prayers throughout the entire period of summer, is something that has no evidence nor an equivalent in the Islamic Sharee’ah. It is known that a resident does not combine the prayers except because of rain or due to sickness, or, according to some jurists, at times of necessity.
As regards combining between the Maghrib and ‘Ishaa’ prayers throughout the entire period of summer, then this is not permissible in our view even if the time of ‘Ishaa’ prayer starts very late before the time of Fajr. So, it is an obligation to perform the ‘Ishaa’ prayer when its time begins. However, some scholars issued a Fatwa that it is permissible to combine the prayers in that case if it is difficult to wait for ‘Ishaa’ prayer, but we do not hold this opinion.
However, even according to the opinion of the scholars who permitted this, the succession (without undue delay) between the two prayers is a condition for combining them and no Nafl [supererogatory] prayer should be performed between the two prayers, because among the conditions for the validity of combining between two prayers is the successiveness between them.
An-Nawawi 
said: “The scholars of our School [i.e. the Shaafi’i School] said: “If one prays between them (the two combined prayers) two Rak’ahs as Sunnah prayer, then the combining between the two prayers becomes void according to our School and this is the view of the majority of the scholars.” In addition to this, Al-Hajjaawi from the Hanbali School of jurisprudence said: “If one prays between them the post-Sunnah prayer or other supererogatory prayers, and not the prostration due to forgetfulness, then the combining between the two prayers becomes void.”
Therefore, you should know that the supererogatory prayer should be performed after finishing the combining of the two prayers.
For more benefit, please refer to Fataawa 123507 and 99424.
Allaah Knows best.