Does raising your hands after tashahud to make dua durin salah invalidate salah? I heard that doing so during salah is bidah.
Some scholars allow raising hands during the prayer for example during a du'a like that of al-Qunoot, but there's no backup for doing so during (or after) tashhahud and before salam.
So considering this bid'ah seems correct. As it was not mentioned that the prophet () raised his hands for du'a in this position. And it is important that acts of worship should be performed in the manner the prophet () showed us else applies:
He who did any act for which there is no sanction from our behalf, that is to be rejected (Sahih Muslim)
"If somebody innovates something which is not in harmony with the principles of our religion, that thing is rejected." (Sahih al-Bukhari)
Nevertheless the prophet said:
The Messenger of Allah (way peace be upon him) said: When any one of you utters tashahhud (in prayer) he must seek refuge with Allah from four (trials) and should thus say:" O Allah! I seek refuge with Thee from the torment of the Hell, from the torment of the grave, from the trial of life and death and from the evil of the trial of Masih al-Dajjal" (Antichrist). (Sahih Muslim 1; 2 and Sunan abi Dawod)
But whether doing so invalidates the prayer needs a further investigation as there are acts and happenings that invalidate the prayer which basically are: In first place we need to know that is in conflict to the necessary conditions for a valid prayer would invalidate the prayer like:
- losing the taharah.
- praying without knowledge of the (correct) prayer time.
- praying with no hidden 'awrah
- praying in the wrong direction (intentionally)
As scholars differed about what is rukn or not of the prayer it is essential for each Muslim to know and apply these arakaan as if we left any of them our prayer would be invalid.
And furthermore scholars defined the following acts as invalidating the prayer:
- Eating and/or drinking while praying (the scholars are in consensus on the matter and say if anybody has done so he must repeat his prayer).
- Speaking while praying and this may apply to saying "oh", "ah" etc. expressing a feeling or whilst crying etc. (we may find some evidences for that in the sunnah like here and here) this also refers to any sound that could sounds like speech, which one could hold, while saying "hatshi" while sneezing when one has caught a cold doesn't fall in this category.
- Moving too much (or too fast) for example if one is looking around himself while praying or changing his actual position by a long walk in manner that a neutral observer wouldn't think he is praying.
- laughing while praying however there's a difference of opinion the majority says this applies to loud laughing (horselaugh) while the hanafis say that this kind of laughing would invalidate both prayer and taharah and quite laughing (which only oneself would hear or feel) would only invalidate the prayer.
- of course if one changed his niyyah and ended the prayer this way (by having the intention to leave the prayer for example) the prayer is invalid.
We are not a fatwa site so I'm not giving you a fatwa whether what you did or do is invalidating the prayer, but you must be aware that it might be considered as a movement which may leave the impression that you are no more praying!