Ahmad ibn Muhammad from Muhammad from Ibn Abi Umayr from Hammad ibn Uthman from Ubaydullah Al-Halabi: Abu Abdillah عليه السلام, who said: "There is no harm in sitting in the Iq'a' position during the prayer between the two prostrations." (sitting back on the heels with the bottom of the toes, and the knees, upon the ground)