If she bid them, they will go barefoot to Jerusalem

From Gaudy Night by Dorothy L. Sayers.  Page 343.

“Harriet rang up the Mitre before breakfast.

      

“Peter, could you possibly come round this morning instead of at six o’clock?”

“Within five minutes, when and where you will. ‘If she bid them, they will go barefoot to Jerusalem, to the great Cham’s court, to the East Indies, to fetch her a bird to wear in her hat.’ Has anything happened?”

“Nothing alarming; a little evidence in situ. But you may finish the bacon and eggs.”

“I will be at the Jowett Walk Lodge in half an hour.”

The allusion, "If she bid them," is from The Anatomy of Melancholy by Robert Burton.