What is the ruling on raising the hands during the opening takbir (iftitah takbir)?

It is sunnah to raise the hands when pronouncing the opening takbir. This is because the Prophet Muhammad (peace be upon him) raised his hands when saying this takbir. (Bukhari, Adhan, 84 [736]; Muslim, Salat, 21-22 [390]; Tahawi, Sharh Ma‘ani al-Athar, 1/195-196 [1157-1170]) According to the Hanafi school, men raise both hands with the palms facing the qibla and the thumbs at the level of the earlobes. Women, on the other hand, raise their hands up to the level of their shoulders. (Marghinani, al-Hidaya, 1/48) In other schools, men also raise their hands up to the level of their shoulders.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu