ssh-add is always asking for passphrase - Automate it on bashrc

I want to add to my bashrc the code:

eval $(ssh-agent -s)
ssh-add ~/.ssh/id_rsa

but it is always asking to **Enter passphrase for /home/User/.ssh/id_rsa:** A friend of mine add the same snippet to bashrc and worked perfectly(without asking for passphrase and showing the message **Identity added: /home/User/.ssh/id_rsa**. How can I do it in a way that I don't have to type the passphrase each time I entry on terminal and show me the info that Identity added?