Shaykh 'Abdul-'Azeez Ibn Baaz
Kitaab Majmoo' Fataawa wa Maqaalaat Mutanawwi'ah li Samaahat vol. 9, p. 336

Are those who are deaf and mute accountable, and do they have to do the obligatory duties prescribed in sharee'ah?

Praise be to Allâh.

Shaykh 'Abd al-'Azeez ibn 'Abd-Allâh ibn Baaz explained that the child who is deaf and mute, when he reaches the age of puberty, is considered to be accountable and expected to fulfil the obligations of prayer, etc. He added that he may be taught what he needs to know by means of writing or signing, because of the general meaning of the shar'i evidence which indicates that these obligations apply to everyone who reaches the age of puberty and is of sound mind. Puberty is reached at the age of fifteen, or when maniy (discharge) is emitted as a result of feeling desire in a dream ("wet dream") or otherwise, and when coarse hair grows around the private parts. In the case of women, there is a fourth sign of puberty, which is the onset of menstrual periods.   

The shaykh called upon the guardian of the one who is deaf or mute to pay zakaah and fulfil other financial obligations on his behalf.  He also has to teach him what he does not know by all possible means so that he will understand what Allâh requires of him and what Allâh has forbidden for him. 

The shaykh quoted as evidence the words of Allâh (interpretation of the meaning):

"So keep your duty to Allâh and fear Him as much as you can" [al-Taghaabun 64:16]

And the hadeeth of the Prophet  (peace and blessings of Allâh be upon him): "If I command you to do a thing, then do as much of it as you can." 

And the shaykh explained that the accountable person who cannot hear or speak, or who becomes unable to hear or speak, should fear Allâh and keep his duty towards Him as much as he can by doing that which is enjoined upon him and abstaining from that which is haraam. He should try to learn as much of the religion as possible, by watching, writing and signing, so that he may understand what is required.