The quality of mercy is not strained. It droppeth as the gentle rain from heaven Upon the place beneath. It is twice blest: It blesseth him that gives, and him that takes. 'Tis mightiest in the mightiest. It becomes The thronèd monarch better than his crown.
William Shakespeare (1564–1616), British dramatist, poet. Portia, in The Merchant of Venice, act 4, sc. 1, l. 181-86 (1600).
Portia, disguised as a man, argues that Shylock should show mercy to Antonio—though shortly afterwards she herself shows little mercy in her dealings with Shylock. (Strained here means "forced," "compelled.").