Chapter 65, "Draco's Oscar Winning Performance".
Lucius: [to Ministry workers, about Draco, who is ranting at the top of his voice] He just wants to see that his guardianship hasn't changed and make sure Narcissa hasn't filed any custody papers.
Draco: Theo said she'd try to get me - she wants my vault! Blaise has been gloating all week that she'll not let me go to Hogwarts!! - he says she'll have me in Beauxbatons wearing a SKIRT!!
Lucius: Now you're just being ridiculous, Draco. She can't do that.
Arthur met them at the floos, wiping tears of laughter off his face, and complemented a grinning Draco on his ploy.
Arthur: Well done, Draco, well done.
Lucius muttered that St. Mungo's closed ward was likely to be contacting him to see if he required their services, but Draco and Arthur just laughed harder.