You were with Harry Holding a book that contains a sock, you then give it to Dobby, Harry then speaks

Harry: Open it.

Dobby opens the book as Draco's father walks the halls, looking for dobby as he says

Draco's father: Dobby!

Dobby: Master has given Dobby a sock.

Draco's father: What? I didn't gi-

Dobby: Master has presented Dobby with clothes. Dobby is free.

Draco's Father looks at Harry and you