Abu Bakr bin Muhammad bin Amr bin Hazm said that the Prophet (peace and blessings be upon him) wrote a letter to the people of Yemen which also contained: "For the tongue too there is the diyah."
The same is reported from Sayyiduna Mu'adh and Sayyiduna Umar (may Allah be pleased with them both).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16248
Zayd bin Aslam (may Allah have mercy on him) said that the Sunnah has been established concerning certain things of a person: "For the tongue there is the diyah, and for the voice, when it is cut off, there is also the diyah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16251
Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "There is the diyah when the tongue is made mute and when the glans of the penis is cut off, and for the two lips too there is the diyah."
This chain is weak; Muhammad bin Ubaydullah al-Arzami and al-Harith bin Nabhan are both da'if (weak).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16252
Sayyiduna Umar (may Allah be pleased with him) said that when the tongue is cut off there is the full diyah for it; if the tongue is damaged to the extent that speech is stopped, there is also the diyah for it; and whatever is less than that, the diyah will be in proportion to it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16253
Sayyiduna Abdullah (may Allah be pleased with him) said that when the tongue is cut off from its root there is the diyah for it, and if there is (partial) damage, the diyah will be correspondingly less.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16254
Amr bin Shu'ayb (may Allah have mercy on him) said that Sayyiduna Abu Bakr (may Allah be pleased with him) gave judgement concerning the tongue: when it is cut off completely there is the full diyah for it, and if a little of it is cut off and speech is not stopped, there is half the diyah for it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16255
Mujahid (may Allah have mercy on him) said: There are 28 letters. If the tongue is cut, the diyah will be in proportion to the number of letters the tongue becomes unable to pronounce.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16257