Hasan and Ibrahim used to leave their hands open during prayer.

Hazrat Ibn Zubair used to leave his hands open during prayer.

Hazrat Ibn Aun says that Hazrat Ibn Sirin was asked whether a person should hold his left hand with his right hand during prayer? He replied that this action was done to avoid blood.

Hazrat Abdullah bin Yazid narrates that I never saw Hazrat Saeed bin Musayyib placing his right hand over his left during prayer; he used to leave his hands open during prayer.

Hazrat Abdullah bin Aizar narrates that I was performing Tawaf with Hazrat Saeed bin Jubair. He saw a man who had placed one of his hands over the other. Hazrat Saeed bin Jubair went to him, made him separate his hands, and then returned.