anyone says Takbirat-ul-Ihram (upon starting Prayer) as "Ya allahu akbar", this person's Salah and the Salah of those who follow will be Batil (null and void). They must repeat the Salah, because this phrase takes the form of an appeal. If he says Takbir as "Ya Allahu Akbar" (Part No. 5; Page No. 303) in the intervals between parts of Salah, his Salah will be deemed sound. He should make up for this mistake by offering Sujud-ul-Sahw (Prostration of Forgetfulness) if it was done out of forgetfulness.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.