Evidence for declaring some parts of prayer as non-obligatory
On September, 30th I heard you speak on Aaj TV, I saw Ghamidi saab a few hours earlier as well answering the same question regarding Salah. And you both said the same thing that only a part of the Salah is fixed and cannot be changed (the earlier part uptill the three quranic versus that are recited plus some supplementary actions and words) and the rest is all discretionary, that if not said do not endanger the validity or the completeness of Salah.
If I understood correctly then among the optional parts are the Tashah-Hud, Durood(Salahwat) and the dua. I have a couple of questions regarding this topic and I would appreciate your answer. Ghamidi saab took care and elaborated on the fact that mostly all Namaz books state the entire and complete procedure of namaaz to be from Sanaa to Dua. And he gave a reason for this as well (as this was the status-quo since those who initially taught Muslims how to pray in the sub-continent) and to conclude he said that what he was saying was right and people should know the difference. Since you agree with him in this opinion, I would like to know all the sources you consulted before you arrived to this opinion. Or if I wanted to 'research' on this topic, what would you suggest I consult?
Regarding the definition of Sunnah that Al-Mawrid representatives give: the consensus among muslims in the world and its authenticity is protected by Allah. In my limited knowledge I believe that muslims from around the world collectively (atleast Sunni Muslims) believe the complete Salah to be from Sanaa to Dua none of them (not even those from Saudi Arabia) clarify the point that you make. (I give reference to Saudi Arabia because people there learnt directly from one another in large numbers as opposed to certain people teaching the masses of the sub-continent). Even in the pamphlet published by Sheikh Abdul Aziz ibn Abdullah Ibn Baz (of the Presidency of Islamic Researchers IFTA and Propagation, Riyadh Saudi Arabia) titled Prophet Mohammad's Manner of Performing Prayers there is no distinction in the parts of Salah such as those that you mention. Other this are the countless books that I've read that teach the Salah and even they do not care to make the distinction that you make. However the pamphlet mentioned above does advise certain supplications(additional) during the salah at different times (sajdah, raku etc).
Keeping this in mind would it be wrong to say that the Sunnah of the muslim ummah is the belief that the complete prayer starts from Sanaa includes Tashah-Hud, Durood and the Dua. And if it is correct then according to your definition this form of Salah becomes the Sunaah. Once again my prior question on what base do you form your view that seems to differ from this Sunnah.
I am going to address that part of your query that questions whether some components of Salah can be considered as optional. These are not necessarily the sources that Dr. Khalid Zaheer sb or Ghamidi sb may have used to arrive at their conclusion regarding which parts of Salah are optional and which are obligatory.
To understand the various differing points of views, one should look at some of the other scholarly works on the issues of Salah. For instance, you can access an online version of Sayyid Sabiq's Fiqh-us-Sunnah. In the first volume of this book, there are two chapters titled 'Obligatory acts of prayer' and 'Sunnah acts of prayer'. If you go through the obligatory acts of the prayers, you will find the list to be close to what Ghamidi sb or Dr. Khalid Zaheer sb mentioned in their discussions although some differences do exist. If you simply browse through the second chapter 'Sunnah acts of the prayer', you will see that scholars have differed in many areas regarding the prayers for the same reason that none of them was instituted by the Prophet (sws) as an obligatory part of the prayer. A point of caveat: When you go through this volume, according to my understanding of the word, 'sunnah' is often employed in the sense of sirah of the Prophet (sws) and not in the sense of a component of Islamic law.
From the same source, one can also see the following opinion regarding supplications after Tashahud (Vol. 1, page 160): 'It is preferred for the person to supplicate after the final tashahud and before making the final salutations (that end the prayer). The person may ask for whatever he wishes of the good of this life and the hereafter. Ibn Mas'ud reported that the Prophet, upon whom be peace, taught him the tashahud and then said, 'Then choose whatever you wish to ask (of llah).'(Related by Muslim.)'
As one can see, the author of this book also considers the parts following tashahud as 'preferred' and not obligatory. The cited saying of the Prophet (sws) clearly informs believers to make supplications that are suited to their own needs. For any act to be classified as an established practice of the Prophet (sws), it must have been instituted by the Prophet (sws) not as an optional act rather as a required part of the prayer. In this instance, we see that not only the Prophet (sws) did not institute tashahud as an obligatory part but many Muslims have also understood it to be not a required part of prayer.
Similarly with respect to the act of tashahud itself, Ibn Rushd, in his famous treatise 'bidayat al mujtahid wa nihayat al muqtasid' writes that Imam Malik, Imam Abu Hanifah and one another group held that tashahud is not required in prayers. While another group comprising of Imam Shafi, Imam Ahmad and Imam Daood holds it to be required. Ibn Rushd then provides the basis of difference for these scholars. For our discussion, the fact that these scholars have differed is sufficient for us to declare that at least it is not something that the Prophet (sws) established as an obligatory act with such clarity that difference of opinion did not exist. This is contrary to recitation of Quran in prayers where such differences of opinion do not exist and it has been understood unanimously as an obligatory part of the prayer as instituted by the Prophet (sws).
From a research point of view, the most important thing in understanding religion is to get accustomed to variance in opinions and diversifying one's perspective accordingly. Study of Quran and prophetic traditions is one of the most beneficial activities especially understanding different scholarly opinions. On particular issue of prayers and other practices, the online version of Fiqh-us-Sunnah is a great resource to get started. Ibn Rushd's book that I have quoted has been translated in Urdu, if you understand Urdu that is, and has been published by Dar-ut-tazkeer in Lahore.
(This question was answered by Muhammad Omer Iqbal.)