The major source we can take as a basis for an answer is this hadith which you may find in sahih [al-Bukhari][1], sahih Muslim on the [authority of Qatadah][2] and [abu Huraira][3] (you may find the last one in sunan [ibn Majah][4] and [Muwatta' Malik][5] but as a mursal hadith of Sa'id ibn al Musayyib who was married to the daughter of abu Huraira) in Jami' at-Tirmidhi [once on the authority of Anas][2] and [on the authority of Qatadah][6], in sunan a-Nasa-i [on the authority of Qatadah][7] and in sunan ibn Majah [on the authority of Qatadah][8]. The common statement from all these ahadith is: > He who forgets the prayer, or he slept (and it was omitted), its expiation is (only) that he should observe it when he remembers it. At-Tirmidhi added comments to his two narrations which also may show the opinions of scholars of his time: He quoted for example a statement of Ali ibn Abi Talib (May Allah be pleased with him) >قَالَ فِي الرَّجُلِ يَنْسَى الصَّلاَةَ قَالَ يُصَلِّيهَا مَتَى مَا ذَكَرَهَا فِي وَقْتٍ أَوْ فِي غَيْرِ وَقْتٍ which means you may pray a prayer you have forgotten or missed at any time no matter if this time was makruh or not. Accoridng at-Tirmidhi Imam Ahmad, a-Shafi'i and Ishaaq have chosen this opinion. In the comment of the other hadith he also added Imam Malik to thiose who have chosen this opinion. An other quote he states is: >وَيُرْوَى عَنْ أَبِي بَكْرَةَ أَنَّهُ نَامَ عَنْ صَلاَةِ الْعَصْرِ فَاسْتَيْقَظَ عِنْدَ غُرُوبِ الشَّمْسِ فَلَمْ يُصَلِّ حَتَّى غَرَبَتِ الشَّمْسُ which describes a man who slept and missed 'Asr prayer and when he woke up at the time of sunset and didn't pray until the dusk. This is the choice of the Kufis (apparently he means abu Hanifa). According to [ibn Hajr][9] in his commentary of sahih al-Bukhari on this hadith: Imam Malik preferred in the case that somebody missed for example 'Asr, than prayed Maghrib and than only remembered having missed the 'Asr prayer, that he should pray 'Asr and afterwards repeat the Maghrib prayer to keep the order! From this we can conclude that you can pray a missed prayer or a prayer you remembered after missing it at any time according most madhabs while some prefer to pray them at a time where prayer is allowed (so according this opinion you shouldn't pray after sobh/fajr fard/farz untill the sunrise). And that the expiation of the missed prayer is the prayer you perform once you remembered it. But I have been taught the following: If the prayers you have missed -for some reasons- are less then 5 prayers one should do them as soon as possible (for example you didn't pray the whole or some prayers on Saturday, so before praying the sobh/fajr fard/farz of Sunday you should pray the day or the prayers of the day you missed), if they are much more one should do them by pairs at the specified time. My last sentence means: If for example you pray your actual dohr/zuhr once you finished you pray two dohr prayers you have missed and so on. <br>This still goes ahead with the teaching of the hadith even if it may contradict somehow, as you should prayer the prayers once you remember them. But if you have missed a lot and have list it would be the best to do them this way to get sure you don't miss any. And don't forget doing repentance for those prayers you are doing qada'/qaza' for! Here some additional fatwas (in Arabic): A question of somebody who [missed a prayer][10] (at time) while performing hajj. A question if [qada'/qaza' of a prayer][11] is "useful" or not: repentance is important! And Allah knows best! [1]: http://sunnah.com/bukhari/9/73 [2]: http://sunnah.com/muslim/5/404 [3]: http://sunnah.com/muslim/5/396 [4]: http://sunnah.com/ibnmajah/2/31 [5]: http://sunnah.com/malik/1/25 [6]: http://sunnah.com/tirmidhi/2/29 [7]: http://sunnah.com/urn/1106190 [8]: http://sunnah.com/ibnmajah/2/32 [9]: http://library.islamweb.net/newlibrary/display_book.php?idfrom=1118&idto=1119&bk_no=52&ID=389 [10]: http://fatwa.islamweb.net/fatwa/index.php?page=showfatwa&Option=FatwaId&Id=110572 [11]: http://fatwa.islamweb.net/fatwa/index.php?page=showfatwa&Option=FatwaId&Id=44733