Islamic Laws : Obligatory acts relating to Namaz » Qiyam (to stand)
Fatawa of Ayatullah al Uzama Syed Ali al-Husaini Seestani
975. If he recites something Mustahab (IN SALAH) while in motion, for example, if he says Takbir while going into Ruku or Sajdah, his Zikr will not be correct but his namaz will be valid. Bi hawli lahi wa quwwati Aqumu wa Aq'ud should be said in the state of rising.