Chanting mantras without initiation is not fruitful. I found few references:
I read shiv puran(English translation by JJ Shastri)
- This mantra is not ineffective even if it is not properly imparted by the preceptor. It is not ineffective even in the case of persons not caring for good conduct and who have not purified the six paths.
Here lord says its not ineffective so it dose not mean it will be effective. May be no negative effects.
Now the best spiritual practise can aspirants do?
- Is it chanting names of deity? 108 Names/Shotas or 1008 Names/Shotras?
- And adding few niyamas once a aspirant gets fluency and pronunciation.
Answers with some references will be appreciated.