Rafa Yadein
I think that I have tried to explain this above with the example of nafil salawat.
Any prayer like that of when an eclipse occurs or asking for rain is just like a dua or a nafil prayer which has a strong tradition in Muslim societies. It is well known that you can make a dua any time or pray any time for anything. I think it would be correct to say it has ijma and tawattur. These actions could arise anytime- we could have a prayer asking for success in exams- because we have the base principle that we pray and make dua in times of need. But no one would have ever started to do extra rafa yadayn if it were not for this hadith. It has no basis in ijma since there is so much ikhtelaf. The action has a basis in the religion as what? As the specific action you do at the start of the prayer. That’s the only definite thing we can say. If it’s not compulsory it’s either bidah or an optional act yes. Unless we have an ijma or tawattur allowing us to say that it’s optional (like extra optional salah) it would be perhaps a bidah since it is being taken from a hadith. And as an addition to my opening paragraphs rafa yadayn is not a worship ritual inherently. It is a method of a worship ritual EG the shariah of it. So to take a ruling from a hadith to add something to this shariah (regardless of if the action itself is already there) is adding to the sharia from khabr ahad. Unless there are certain actions that come from khabr ahad. I find no problem to be honest to accept ahadeeth like this since historical principles seem to tel us there would be no need to fabricate something like this no?