Open Facebook and go to your profile
Tap or click Friends
Tap or click the pencil icon or More
Select Edit Privacy
Under Friend List, choose Only me
Save the changes
If using the Facebook app, open the menu and go to Settings & privacy
Tap Settings
Go to Audience and visibility
Tap How people find and contact you
Set Who can see your friends list to Only me
Check your profile from another account to confirm the friend list is hidden