ROUTINE IS NECESSARY IN QAZA NAMAZ
Rule: For a Sahib-e-Tarteeb, meaning for those who have less than six Namaz in total of Qaza to pray, then when remembering and there being enough time to pray the Qaza, he prays his Ada instead then this Namaz will not count. This means he will still have to pray the Ada Namaz again. If he continued praying the Ada Namaz and missed the Qaza until he has prayed the sixth Namaz and then all the Namaz will be correct as he will no longer be Sahib-e-Tarteeb any more and if in between he prays one Qaza, then all the Ada will not count.
Rule: Tarteeb meaning routine is necessary for the missed Namaz and the Ada Namaz as long as there are less than six missed Namaz and hence first the Qaza should be prayed then the Ada. For example if today someone's Fajr, Zohr, Asr and Maghrib became Qaza then he cannot pray the Isha Namaz until he has prayed the Qaza for the four Namaz in sequence first.
Rule: If there isn't enough time to pray the Ada and all the Qaza Namaz then pray as many Qaza and the Ada as possible and for the rest, Tarteeb can be missed, for example, if both the Farz of Isha and Witr became Qaza and in Fajr you only had time to pray five Rakats then you pray three Rakats of Witr and two of Fajr, and if you only had time for six Rakats then pray the Qaza of Farz Isha and pray two Rakats Farz of Fajr [Shareh Wiqaya].
Rule: If six Namaz became Qaza and as soon as the time for the sixth is finished there is no longer a need for Tarteeb and now regardless of remembering and having time if you pray the Ada Namaz it will count. Whether the Qaza have occurred all in one go meaning six Namaz together or by six in a few days, for example, your Fajr became Qaza for six days and you continued praying Ada and totally forgot about the Qaza then the same rule applies and you are no longer a Sahib-e-Tarteeb [Radd-ul-Mohtar].
Rule: As soon as six Namaz became Qaza and the time for the sixth Namaz has gone then Tarteeb is no longer Farz anymore, whether all the missed Namaz are old or some are recent and some are old , meaning if you missed a month's Namaz and then started praying again and again missed a couple you are still no longer a Sahib-e-Tarteeb as you have more than six Qaza in total to pray [Radd-ul-Mohtar].
Rule: When due to having more than six Qaza the Tarteeb is no longer necessary then if some of the Qaza is prayed and there are less than six Qaza remaining in total then you will still no longer be Sahib-e-Tarteeb until all the Qaza is prayed, and when this is the case you will become Sahib-e-Tarteeb again [Shareh Wafaya, Alamgiri, Durr-e-Mukhtar, Radd-ul-Mohtar].
Rule: Just as six or more Qaza Namaz clears the necessity for routine for the Ada and Qaza Namaz, there is also no need for routine for the Qaza Namaz, meaning that the remanding Qaza can be prayed in whichever sequence deemed suitable, for example, if someone missed a full month's Namaz and then he prayed them first the thirty Farz of Fajr then the thirty Namaz of Zohr etc. and this would also be acceptable and the Namaz will count [Alamgiri]. Whoever has the responsibility of praying Qaza Namaz although it is necessary for them to be prayed as soon as possible they can be delayed due to responsibilities towards the family, or work etc. and whenever he gains some free time he should pray the Qaza until they are all complete [Durr-e-Mukhtar].
Rule: Qaza Namaz is more important than the Nafl Namaz and therefore when you pray the Nafl instead you should pray any Qaza you may have left, however, do not replace the Tarawih or the twelve Sunnat-e-Maukidah (in the day).
Rule: For those who have the responsibility of many years Qaza and they cannot remember exactly how many then they should make the intention that "I am praying the first Qaza of Fajr or Zohr or Asr, that is due from me" and complete all the Qaza like this until they are certain that they have none left to perform.
