What is the ruling on someone who added a prostration to the Dhuhr prayer and did not sit for the Tashahhud? Is he required to perform a pre-emptive prostration (sujud qabli) due to the deficiency, and a post-emptive prostration (sujud ba'di) due to the addition?

If someone makes two mistakes (sahw) in their prayer, one that necessitates the prostration of forgetfulness (sujūd al-sahw) before the salām and another that necessitates it after, then a single prostration of forgetfulness before the salām suffices. This is because it is earlier and more emphasized, and the second one is dropped because the first renders it unnecessary and takes its place.