How to Run SCP Without Password Prompt Interruption

# ssh-keygen -t rsa -b 4096 -C "root@localhost"

Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
33:4c:b1:a1:b0:f7:3a:85:0c:85:b9:6b:eb:c6:69:8b root@localhost
The key's randomart image is:
+--[ RSA 4096]----+
| .o. o |
| o+ . + |
| o.o o |
| .+ = |
| .o S |
| o o o |
| o oo |
| .* . |
| E+o. |
+-----------------+

# ls -l .ssh/

total 8
-rw-------. 1 root root 3239 Aug 13 13:11 id_rsa
-rw-r--r--. 1 root root 736 Aug 13 13:11 id_rsa.pub

Once the the public key is generated, copy the .pub file as authorized_keys under .ssh directory under user home for the user in destination server. Once done, try to do ssh which will connect without password
# cat .ssh/id_rsa.pub | ssh root@server2 'cat >> .ssh/authorized_keys'
# scp test_file.txt root@server2:/tmp/
test_file.txt 100% 20 0.0KB/s 00:00