Guru Periya Nambi asked Srimad Ramanuja to go to Thirukoshtiyur Nimbi to learn from him the secret to attain Moksha. Ramanuja went to Thirukoshtiyur Nambi’s house and prostrated before him and put up his request to him. Thirukoshtiyur Nambi looked at him and said, “I do not think you are eligible to know about it, as of now. You go and come back again after some time.” Ramanuja returned to Srirangam with much disappointment and made eighteen trips to Thirukoshtiyur by walk and each time he was sent back.
Looking at Ramanuja’s persistence one day Thirukoshtiyur Nambi said, “I will now incite the Ashtakshara Maha Mantra which will free the person who recites it from cycle for birth and death but, you have to keep it a secret never reveal it to anyone. If you do so you will go to hell.”
Ramanuja was incited with the mantra. Ramanuja’s face was radiant and he was very happy. Next morning instead of returning to Srirangam he went to Thirukoshtiyur temple. On the way he called out to the people and told them to come to the temple and he would gift them a valuable gem which would give them Eternal Bliss. Ramanuja climbed up the steps and reached the top of the temple Gopuram.
He told the people that he was going to tell them about a Mantra that would free them from the circle of samsara. He loudly chanted “Om Namo Narayanaya” and asked the people to repeat it. People were all enthralled and repeated it.
Thirukoshtiyur Nambi came to know about it and he fumed with rage. He came to the temple and shouted, “By giving initiation to you I have committed a sin. You are a traitor you will go to hell.”
Ramanuja replied politely, “Acharya! I know that I will go to hell for not abide your command. But if thousands of people would be benefited by chanting this mantra, I would not mind going to hell.”
When Nambi heard this he hugged Ramanuja and appreciated his broadmindedness and blessed him.
What is so special about this Maha Mantra???
Hiranya Kashyapu had told his wife, Kayadhu that he would go to Mount Kailasa and do penance, may be it will take some years for him to come back. But he returned back after a few day, Kayadhu was surprise but did not ask him the reason then. After a few days when Hiranya Kashyapu was alone with Kayadhu one night, she asked him the reason for him to return back without performing penance. Hiranya Kashyapu tells his wife the reason for him to abort penance was two sparrows. When he sat in the seat of silence two sparrows chanted “Om Namo Narayanaya” and he was disturbed and in a fit of anger he went to kill those two birds which flew away. Unable to concentrate he ceased practicing penance and came back.
In reality the two sparrows were Sage Narada and Sage Parvata who were assigned to disguise as birds and disturb the penance. Now, when Hiranya Kashyapu was explaining this to his wife he copulates with her who was in her ovulation period and she conceived. The fetus in the womb of the mother gradually developed and happened to be a great devotee of Maha Vishnu.
The Mantra “Om Namo Narayanaya” in the mind of Hiranya Kashyapu when he was united with Kayadhu brought Prahlada to the earth. This incidence is mentioned in Narasimha Purana.