Musannaf Ibn Abi Shayba 18:230

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: Ibn Abi Najih informed me, from Mujahid, he said: If the palm is severed, then [the compensation is] fifty camels. If what remains of the entire hand or the forearm is severed, or if half of the forearm is severed, then half of the compensation of the hand is also [due], which is twenty-five. If it was only severed from a portion of its forearm, or the forearm after the palm, Mujahid said: He says that is half of the compensation of the hand. If what remains of the whole is severed, then it is a wound for which he is treated.