Who said stone walls do not a prison make nor iron bars a cage?

Richard Lovelace (1618-1658) to Althea from prison(1649. The whole verse reads

Stone walls do not a prison make,

Nor iron bars a cage;

Minds innocent and quiet take

That for an hermitage;

If I have freedom in my love,

And in my soul am free,

Angels alone that soar above

Enjoy such liberty.