In OoP:
"Remember my Last!"

Elsewhere:
"But she took you."
...and thereby sealing... something or other?

In HBP-3:
"Now, as you already know, the wizard called Lord Voldemort has returned to this country. The Wizarding community is currently in a state of open warfare. Harry, whom Lord Voldemort has already attempted to kill on a number of occasions, is in even greater danger now than the day when I left him upon your doorstep fifteen years ago, with a letter explaining about his parents' murder and expressing the hope that you would care for him as though he were your own."
[....]
"You did not do as I asked. You have never treated Harry as a son. He has known nothing but neglect and often cruelty at your hands. The best that can be said is that he has at least escaped the appalling damage you have inflicted upon the unfortunate boy sitting between you."
[....]
"The magic I evoked fifteen years ago means that Harry has powerful protection while he can still call this house 'home.' However miserable he has been here, however unwelcome, however badly treated, you have at least, grudgingly, allowed him houseroom. This magic will cease to operate the moment that Harry turns seventeen; in other words, at the moment he becomes a man. I ask only this: that you allow Harry to return, once more, to this house, before his seventeenth birthday, which will ensure that the protection continues until that time."