Find all files in a directory which contain "pass" or "password", ignoring case:
grep --color=auto -rnw '<dir>' -ie "password\|pass" --color=always 2>/dev/null
Find all files in a directory which contain "pass" or "password" in their name, ignoring case:
find / -name "*pass*" 2>/dev/null
find / -name id_rsa 2>/dev/null