Mahathir’s definition of a Malay

‘Mahathir simplified the meaning of being a Malay by saying to be a
Malay, one has to speak the Malay language, follow the Malay customs and
be a Muslim…. To be a Malay, said Mahathir, is no more an ethnic thing
as today it is more of a legal matter.’
 
What or who should be the authoritative source of what is a Malay?
Singapore’s has its own definition of what is a Malay. According to