The different supplications recited in qa’da have many issues that do not go well with Quran. It is not unlikely that this component of Salat, whether entirely or partially, was added later on, and may not have had the sanction of Prophet. Here is the reason:
The salat according to Quran ends in prostration, not qa’da:
[4:102] If you are with them and hold the contact prayer for them, then let a group from amongst them stand with you and let them bring their weapons; when they have prostrated then let them stand guard from behind; let a group who has not yet contacted come and contact with you, and let them be wary and let them bring their weapons with them.
Moreover, Quran tells us that after prostration, we are to recite His tasbeeh:
[50:40] From the night glorify Him, and after prostrating.
The appropriate supplication after prostrating should be to glorify God. Quran also tells that Salat is to commemorate God alone, and at places of Salat (mosques), no one else should be called or invoked:
[72:18] And the mosques, one and all, belong to God alone. So, do not call upon anyone along with God.
The prayer of attahiyat, which inherently has nothing wrong in it, is not an appropriate prayer to be included in Salat, as per the framework of Quran (except for the first four words). It patently clashes with the above verses, especially verse 72:18.
Please also keep in mind that as muslims we are repeatedly told by Allah not to discriminate among prophets. All prophets are equally important and honorable for us (2:285, 4:152, 3:84). It is not appropriate to select one or two prophets of your liking and include their praise and prayer for them in salat, and leave out the rest. Both the attahiyat and durud violate this important principle.
If you do want to send blessings on the Prophets in Salat, it would be more appropriate to select from the prayers that Prophet has taught us through Quran. For instance the following prayer (given in 37:180-182) starts and ends with glorification of God (which we are commanded to do after prostration in 50:40), and also sends blessings on all Prophets. Therefore, no discrimination is involved:
سبحن ربك رب العزة عما يصفون
وسلم على المرسلين
والحمد لله رب العلمين
Our assumptions about the authenticity of different rituals that we conveniently all categorize under “Sunnah” are often far-fetched and at variance with Quran. Since they are all based on hearsay, it is not surprising that they often contradict with Quran. These assumptions, when remain unchecked and unscrutinized have the potential to distort our beliefs and rituals, and may make our practices at odds with what Allah has commanded us. Therefore, it is our responsibility to ensure that all our rituals are in strict compliance with the word of Allah delivered to us through Prophet Muhammad PBUH.