Does forgetting to say "Sami'a Allahu liman hamidah" (Allah hears those who praise Him) in the third rak'ah make the subsequent rak'ah the third?

Reciting the Tasmi' (saying "Sami'a Allahu liman hamidah" - Allah hears those who praise Him) is a Sunnah according to the majority of scholars, and a duty of prayer according to the Hanbalis. There is no difference in its ruling whether it is omitted from the first, third, or fourth rak'ah. Thus, prayer is not invalidated by its omission due to forgetfulness.