Crossing the Hands in Prayer (Takfir)
The Messenger of Allah has said, “Perform your prayers as you see me performing my prayers.” Therefore, crossing the hands makes the prayers void in the Imamiyyah (those who believe in the 12 imams who succeeded the Noble Prophet as appointed by Allah) school of thought, since it is deemed as the habit of the Magians (Majus).However, in the Hanafi and Shafi΄i schools, it is recommended (mustahhab) to cross the hands. Nevertheless, the two schools differ slightly in the hand posture; the Shafi΄i school says to cross the right hand on top of the left above the belly, while the Hanafi says to hold the hands below the belly.
 Takfir comes from the Arabic word for “covering,” and since crossing the hands covers part of the chest it is called takfir.
 Magians are people who consider fire as the purest and noblest element, and worship it as an emblem of Allah. They are mentioned in the Noble Quran, 22:17
 Al-Kulayni, al-Kafi, Vol. 3, 336; al-Tusi, al-Ta’dhib, Vol. 2, 84 and 309