Mohammad in his letter Not right for other religions to use 'Allah' argues that it is not proper for those of other religions to use 'Allah'. I beg to differ.
I am of the Sikh faith. Ever since the founding of the faith more than 500 years ago, Sikhs have used 'Allah' to refer to God as well as many other terms. The word 'Allah' appears repeatedly in their Holy Book. The religion is epitomised by the Mool Mantar that appears as the first verse in the Sikh Holy Book.
The translation of the Mool Mantar corresponds to what Mohammad wrote on 'Allah'. Sikhism believes that there is Only One God and Truth is His Name, He is the Creator and Protector, Fearless, Has no Enmity, Is the First Entity, Is Eternal and without Incarnations.
In the Sikh Holy Book, it is to be found the following verse:
"Aval Allah noor upaa-i-aa, kudarat ke sabh bande,
ayk noor te sabh jag upaji-aa, kaon bhale ko mande."
Kabir, SGGS pg 1349-50
In the beginning God brought forth His light.
From His creative power came all beings.
From One light the entire universe came forth.
So who is good and who is bad?
I do believe that as a Sikh I cannot be denied my prayer and my right to refer to God as 'Allah'. It is a right as given to me in my prayers and enshrined in the Sikh Holy Book.