“You might ask — and with good reason — why it had to be so. Why could some Wizarding family not have taken you in? Many would have done so more than gladly, would have been honored and delighted to raise you as a son.

“My answer is that my priority was to keep you alive. You were in more danger than perhaps anyone but myself realized. Voldemort had been vanquished hours before, but his supporters — and many of them are almost as terrible as he — were still at large, angry, desperate, and violent ...
_{Harry Potter and the Order of the Phoenix (Chapter 37: The Lost Prophecy)}

“I knew that Voldemort’s knowledge of magic is perhaps more extensive than any wizard alive. I knew that even my most complex and powerful protective spells and charms were unlikely to be invincible if he ever returned to full power.

“But I knew too where Voldemort was weak. And so I made my decision. You would be protected by an ancient magic of which he knows, which he despises, and which he has always, therefore, underestimated — to his cost. I am speaking, of course, of the fact that your mother died to save you. She [Petunia] gave you a lingering protection he never expected, a protection that flows in your veins to this day. I put my trust, therefore, in your mother’s blood. I delivered you to her sister, her only remaining relative.”
_{Harry Potter and the Order of the Phoenix (Chapter 37: The Lost Prophecy)}

“You might ask — and with good reason — why it had to be so. Why could some Wizarding family not have taken you in? Many would have done so more than gladly, would have been honored and delighted to raise you as a son.

“My answer is that my priority was to keep you alive. You were in more danger than perhaps anyone but myself realized. Voldemort had been vanquished hours before, but his supporters — and many of them are almost as terrible as he — were still at large, angry, desperate, and violent ...
_{Harry Potter and the Order of the Phoenix (Chapter 37: The Lost Prophecy)}

“I knew that Voldemort’s knowledge of magic is perhaps more extensive than any wizard alive. I knew that even my most complex and powerful protective spells and charms were unlikely to be invincible if he ever returned to full power.

“But I knew too where Voldemort was weak. And so I made my decision. You would be protected by an ancient magic of which he knows, which he despises, and which he has always, therefore, underestimated — to his cost. I am speaking, of course, of the fact that your mother died to save you. She [Lily] gave you a lingering protection he never expected, a protection that flows in your veins to this day. I put my trust, therefore, in your mother’s blood. I delivered you to her sister, her only remaining relative.”
_{Harry Potter and the Order of the Phoenix (Chapter 37: The Lost Prophecy)}