Musannaf Ibn Abi Shayba 18:212

Abu Bakr narrated to us, he said: Muhammad bin Bakr narrated to us, from Ibn Jurayj, he said: Abd al-Aziz informed me that in a letter from Umar bin Abd al-Aziz, regarding Umar bin al-Khattab, concerning the tongue: If it is completely eradicated, the full blood money (diyah) is due. And whatever is injured of the tongue such that it reaches the point of preventing speech, then the full blood money is due for it. And whatever is less than that, then it is according to its proportion.