DUMB, The. Arabic abkam ابكم
The intelligible signs of a dumb person suffice to verify his bequests and render them valid; he may also execute a marriage contract, or give a divorce, or execute a sale or purchase, or sue or incur punishment by signs, but he cannot sue in a case of qisas, or retaliation for murder. This rule does not apply to a person who has been deprived of speech, but merely to one who has neem bron dumb. (Hidayah, vol. iv. P. 568.) A dumb person can also acknowledge or deny the faith by a sign.
Based on Hughes, Dictionary of Islam