When is the position for raising the hands in prayer upon rising from bowing: Is it after saying "Sami' Allahu liman hamidah" or while saying "Rabbana wa laka al-hamd"?

The hands are raised when rising from rukūʿ (bowing). Scholars have differed on the timing of this raising, holding two views: The first is that one should begin raising them at the start of lifting the head from rukūʿ, which is the more probable view, due to the apparent meaning of the hadiths and because "after he raises his head" means "after he begins to raise [his head]". The second is after he has fully straightened up from rukūʿ. Imam Ahmad acted upon this second view. Both matters are permissible.