What is the authenticity of the addition by Muhammad ibn Ishaq regarding the details in the tashahhud?

The Shaykh : If we look at the chain of this hadith, we can say that it is hasan (good), not sahih (authentic). Why? Because Muhammad ibn Ishaq explicitly stated that he heard it. However, in his biography, two defects are mentioned: the well-known defect is tadlis (concealment of a defect in a chain), and the less well-known defect, which students of this science often do not notice, is that he sometimes narrates munkar (denounced) reports and contradicts the trustworthy narrators in them. This is the reality in our hadith here. It is known that a complete part of this research is that the hadith narrated by Ibn Ishaq ends with Abdullah ibn Mas'ud. The hadith of Abdullah ibn Mas'ud exists and is narrated in the two Sahihs and other sources without the addition brought by Ibn Ishaq, which is the detail between the first tashahhud and the final tashahhud. Therefore, this awareness and attention to the other narrations or other chains regarding Abdullah ibn Mas'ud give the researcher the alertness to be cautious of Ibn Ishaq's singularity in this addition, because it will either be called shadhdh (anomalous), if we consider that the original narrator is trustworthy, or we will say it is munkar (denounced), because Ibn Ishaq has a slight criticism regarding his memory and precision. In any case, this is a terminological matter and the issue is easy. The important thing is that such an addition from Ibn Ishaq is not accepted due to its contradiction with the narrations of the trustworthy narrators. This is my view on this matter. Perhaps if Ibn Ishaq had been trustworthy without any criticism, we would have said, by Allah, that an addition by a trustworthy narrator is acceptable. But that is not the case here, as I mentioned earlier.
The student : I mean, my Shaykh...

The Shaykh : I do not know where you have traced this hadith, do you remember?
The student : Yes, my Shaykh, in al-Da'if (The Weak Hadiths), it is around eight thousand, five hundred and sixteen.

The Shaykh : Eight thousand? We did not reach that!
The student : Or five thousand, eight hundred and sixteen...

The Shaykh : Yes, let me look. In his statement, "in the middle of the prayer and at its end, on his left hip," this is tawruk (sitting on the left hip), and there is no tawruk in the middle.